ESTIMATION OF MERCURY EMISSIONS
FROM WATER BODIES IN XIAMEN AREA
International Summer Water Resources Research School
(VVRF05)
LTH, Lund University, Sweden
Xiamen University, China
Instructor: Dr. Jinjing Luo (Associate Professor)
Assistant: Jinlan Li (Graduate Assistant)
Caroline Säfström
2008
PREFACE
This report is a part of the course International Summer Water Resources Research School 2008
that is given by LTH, Lund University. The literature study was undertaken in Lund, Sweden
with assistance of Water Resources Engineering, LTH, Lund University whereas all of the
sampling and laboratory parts were done in Xiamen, China with the help of Environmental
Science Centre, Xiamen University.
Dr. Jinjing Luo has been the instructor for the project and assistant in the laboratory was Jinlan
Li. The laboratory work has been performed by Jinlan Li together with the students Wenwen
Chen, Caroline Säfström and Yao Wang.
I would like to thank everyone involved in this Summer Research School at Xiamen University
and Lund University for making an experience like this possible. A special thank you is directed
to the group which I have been working together with; Dr. Jingjing Luo, Jinlan Li, Wenwen Chen
and Yao Wang for their great optimism and kindness which have made the project not only
educational but also made sure there were laughter in the laboratory each day. A sincere thank
you as well to Vera Shi, whom I would not have been able to sort out all forms and permissions
with out – thank you! Finally I would also like to thank all the nice students from Xiamen
University whom have arranged activities throughout our stay, it has been much appreciated!
ABSTRACT
Mercury poses an environmental threat due to its toxicity and persistence in the environment and
the aim of this project has been to increase the knowledge of natural sources to inorganic
mercury emissions in local regions around Xiamen, China. In order to estimate mercury
emissions from water bodies in Xiamen area, water and air samples were collected and analysed
from different water bodies, two lakes and one wastewater station as well as rainwater, situated in
Xiamen University campus or nearby. The set out was to answer the question: which
concentrations of natural inorganic mercury can be found in local water bodies around Xiamen?
Only two species of inorganic mercury, dissolved gaseous mercury (DGM) and total mercury
(THg), was measured due to the limited time at hand and that the method used for analysis had
to be altered during the project due to contaminated hydrochloric acid. All of the samples was
analysed according to Method 1631, Revision E: Mercury in Water by Oxidation, Purge and
Trap, and Cold Vapor Atomic Fluorescence Spectrometry (EPA, 2002).
The following concentrations of mercury were found at the different locations;
-
In Furong lake, situated inside Xiamen university campus area, DGM concentrations in the
water reach from 0.02 to 0.3 ng/L and in the air THg concentrations were from 0.004 to 0.08
ng/L.
-
For the pond inside Nanputuo temple water concentrations of DGM were 0.1 to 0.2 ng/L
and air concentration of THg from 0.01 to 0.02 ng/L.
-
The wastewater contained DGM concentrations of 0.2 to 0.4 ng/L and the air sample at the
wastewater station 0.01 ng THg/L.
-
The rainwater had a mercury concentration of 0.1 ng DGM/L and the air inside a conference
room in the Ocean building at Xiamen University contained 0.002 ng THg/L.
It is indicated from the results that the lakes, wastewater, rainwater and conference room air are
not polluted by mercury when compared to average values found in the literature. The water
bodies does however serve as sources of mercury to the air since mercury concentrations
measured in the air above the water bodies all were higher than the average value expected to be
found in the air. There are although also other sources adding mercury to the air in the nearby
area apart from the water bodies, i.e. a power station.
Keywords: mercury, DGM, THg
ii
CONTENTS
1
INTRODUCTION ...................................................................................................................................................... 2
1.1
1.2
1.3
2
AIM ...................................................................................................................................................................................................2
PROBLEM FORMULATION ..................................................................................................................................................2
LIMITATIONS ..........................................................................................................................................................................2
BACKGROUND – MERCURY ................................................................................................................................ 2
TOXICITY ..................................................................................................................................................................................3
SOURCES ...................................................................................................................................................................................3
ATMOSPHERIC DEPOSITION..............................................................................................................................................4
2.3.1 Flux........................................................................................................................................................................................ 4
2.4
SPECIES......................................................................................................................................................................................5
2.5
PREVIOUS STUDIES ...............................................................................................................................................................6
2.1
2.2
2.3
3
METHODOLOGY ...................................................................................................................................................... 6
3.1
3.1.1
3.2
THEORY ....................................................................................................................................................................................7
Method used ...................................................................................................................................................................... 7
ANALYSIS...................................................................................................................................................................................8
4
RESULTS .................................................................................................................................................................... 16
5
DISCUSSION............................................................................................................................................................. 19
5.1
6
IMPROVEMENTS.................................................................................................................................................................. 20
CONCLUSIONS ....................................................................................................................................................... 20
REFERENCES .................................................................................................................................................................. 21
7
APPENDICES ........................................................................................................................................................... 22
7.1
7.1.1
7.1.2
7.1.3
7.1.4
EVALUATION ........................................................................................................................................................................ 22
Laboratory work ............................................................................................................................................................ 22
Team work and report ................................................................................................................................................ 22
Xiamen University ....................................................................................................................................................... 22
In total ............................................................................................................................................................................... 22
iii
1 INTRODUCTION
Mercury poses an environmental threat due to its toxicity and persistence in the environment.
Apart from anthropogenic sources, such as mercury mining and fired power plants, there are also
natural sources of mercury emissions. Examples of natural sources are the mineral cinnabar and
flux from water bodies. The natural source of mercury from water bodies has been the focus for
this project.
Due to the properties of low solubility in water and high volatility, mercury is re-emitted from
previously deposited elementary mercury through gaseous evasion between the water-air
interface. The elementary mercury present in the atmosphere have a long residence time, one
year, and is therefore capable of being transported over vast areas.
In order to estimate mercury emissions from water bodies in Xiamen area, water and air samples
were collected and analysed from different water bodies in the local area. Only inorganic mercury
was measured due to the limited time at hand.
1.1 AIM
The aim of this project has been to estimate natural inorganic mercury releases from water
surfaces in different local regions, such as e.g. an unpolluted freshwater lake, and a contaminated
water body. Most mercury studies have focused on the magnitude of anthropogenic emissions of
mercury and therefore this project has been aimed to increase the knowledge of natural sources
to inorganic mercury emissions in local regions around Xiamen, China.
1.2 PROBLEM FORMULATION
The set out has been to answer the following question;

Which concentrations of natural inorganic mercury are found in local water bodies
around Xiamen?
1.3 LIMITATIONS
The combination of contaminated hydrochloric acid and unstable results that prompted for more
than one sampling from the same location made it, due to lack of time, not possible to analyze all
of the different types of inorganic mercury originally intended. Therefore dissolved gaseous
mercury (DGM) and total mercury (THg) were the only types of inorganic mercury analysed.
In analysis 1 to 4 the intended volume of 800 mL was used for the analysis. In analysis 5 to 8
however the analysed volume was diminished to 600 mL due to limited access to bubblers in the
laboratory.
2 BACKGROUND – MERCURY
In this chapter some of the toxic properties of mercury will be presented, sources for mercury as
well as atmospheric deposition and flux rates. Different mercury species will be introduced and
also results from previous studies regarding mercury in water bodies.
2
2.1 TOXICITY
Mercury poses an environmental threat due to its toxicity and persistence in the environment.
Neurological problems, myocardial infarction and autism have been connected exposure to
inorganic mercury and methyl mercury, the toxicity does however depend on the chemical form
of the mercury (Muresan, Cossa, Richard, & Burban, 2007; Li, et al., 2008). The recommended
hygienic limit value for mercury vapour is 0.03 mg per m3 (Nationalencyklopedin, 2008).
Biological processes in the environment can transform inorganic mercury to methyl mercury,
which is highly toxic and also capable to bio accumulate more than a million fold in aquatic food
chains. Neither the blood-brain barrier nor placenta is able to protect the human brain respective
foetus from this form of mercury, methyl mercury, resulting in that the human brain respective
foetus are exposed to a possible neurotoxin (Schroeder & Munthe, 1998; Fantozzi, Ferrara,
Frontini, & Dini, 2007; Nationalencyklopedin, 2008).
2.2 SOURCES
Mercury is unusual in the crust and is present in an average concentration of 0.08 g per ton, i.e.
1 000 times less than e.g. zinc and copper. Large deposits exists in, inter alia, Spain, Slovenia,
USA and China. Altogether it has been estimated that there are 240 000 tons of mercury existing
in the world and each year approximately 3 400 tons of mercury is produced through mining.
Mercury is present in the atmosphere and oceans as well in concentrations of 1 to 2 ng per m 3
respective 0.5 to 3 ng per litre (Nationalencyklopedin, 2008). The mean north Atlantic level of
TGM is 11.5 pmol m-3, where GEM constituted more than 98 percent of total gaseous mercury
(Slerm & Langer, 1992).
Apart from anthropogenic sources of mercury, such as mercury mining, fired power plants and
chloralki industry (Li, et al., 2008), there are also natural sources. Examples of natural sources of
mercury are; the mineral cinnabar, emissions from volcanoes, soil layers and water bodies
(Schroeder & Munthe, 1998). A study has estimated that the yearly emissions of mercury from
natural sources are approximately 3 000 ton (Nriagu, 1989). Mercury is also re-emitted from
previously deposited elementary mercury (Hg0) through gaseous evasion. Mercury is thought to
be released from natural sources mainly as elementary mercury vapour but some is likely also
released as mercury bound to particulate matter or aerosols. The mercury specie dimethyl
mercury (DMM, (CH3)2Hg) has a short residence time in the atmosphere due to reaction with
hydroxyl oxidants (Schroeder & Munthe, 1998). An overview of the deposition cycle for mercury
can be found in Figure 2.1, below.
There is a transport from water to the atmosphere of DGM since it has low water solubility, 60
μg per litre, as well as high volatility, Henry coefficient < 0.3 (Fantozzi, Ferrara, Frontini, & Dini,
2007).
3
ATMOSPHERE
CLOUDS
In-cloud processes
Transformations
Air
concentrations
Transport and diffusion
Scavenging
Emissions
Gas/particle
(including re-emission of
previously deposited Hg)
Anthropogenic
sources
partitioning
Natural
sources
Gas
exchange
Dry
deposition
Wet deposition
EARTH’S SURFACE
(water, soil, vegetation)
FIGURE 2.1 Overview of the atmospheric emissions to deposition cycle for mercury. Adapted from Schroeder (1998).
2.3 ATMOSPHERIC DEPOSITION
Atmospheric deposition of mercury has increased 2- to 20-fold during the last centuries, partly
due to industrialisation, and is the dominating source for mercury in water bodies (Schroeder &
Munthe, 1998; Meili, et al., 2003; Pal & Ariya, 2004; Sprovieri, Pirrone, Landis, & Stevens, 2005).
The environmental effect from mercury depends on which species of mercury that are present,
which is a result of physical, chemical and biological factors (Ullrich, Tanton, & Abdrashitova,
2001). Elementary mercury remains in the atmosphere for months before deposition and can
therefore be spread over a vast area (Schroeder, Munthe, & Lindqvist, 1989; Wang, Shi, & Wei,
2003). Mercury differs from other metals since its tendency is to exist in ambient air instead of in
solid phase. Its tendency to be remitted to the air even though deposited to surfaces is important.
This combined with its inert property, i.e. not to react with other air particles as well as having a
low solubility in water results in a residence time of one year (Schroeder & Munthe, 1998;
Muresan, Cossa, Richard, & Burban, 2007).
2.3.1 FLUX
A study in Sweden estimated the average net emission fluxes of mercury from lakes. The results
showed that during the warm season, i.e. a temperature of 12-23°C, the daytime flux was 3-20 ng
per hour and m2, whereas in the night time flux was two to three times smaller (Xiao, Munthe,
Schroeder, & Lindqvist, 1991). This can be compared to a study performed of sub-basins of the
Negro River basin in Brazil, where the evasive flux of DGM were 0.09 to 14 μg per m2 and year
(average 3.9 μg per m2 and year) (Silva, Jardim, & Fadini, 2006). The following relation, equation
below, combined with the mass-transfer of CO2 across the air-water interface, was used in the
study in French Guiana, to estimate lake-air transfer of mercury (Muresan, Cossa, Richard, &
Burban, 2007).
4
Ca = concentration of GEM
Cw = water concentration of DGM
K = mass transfer coefficient of Hg0
H = Henry coefficient, temperature-corrected
The flux of dissolved gaseous mercury was also calculated in another study at the water-air
interface in the Negro River basin, in Brazil, with starting point in Fick’s law, below.
F = DGM flux
- = invasive flux in respect to the atmosphere
+ = evasive flux in respect to the atmosphere
ΔC =concentration gradient
k = transfer velocity
Catm/measured = atmospheric gaseous mercury concentration
Cwater/measured = water gaseous mercury concentration
H = Henry’s law constant
Both wet and dry processes are involved in the removal of the different mercury species in the
atmosphere (Schroeder & Munthe, 1998).
2.4 SPECIES
The elemental and dimethylated forms of mercury are volatile and as a result this property
increases the spread of mercury emissions (Xiao, Munthe, Schroeder, & Lindqvist, 1991). The
dominating form of mercury in the atmosphere is the elemental form, i.e. oxidation state 0 (95
percent is Hg0), and oxidation state +2; however mercury can also exist in oxidation state +1,
even though this is extremely rare. Seven isotopes of mercury exist, which makes it suitable to
spectrometric analysis (Schroeder & Munthe, 1998; Nationalencyklopedin, 2008).
The three dominating species of mercury behave differently in the atmosphere in respect to
transportation characteristics; Hg0 can be transported over 10 000 km, whereas HgII will be
removed within tens or hundreds of km within their origin, and particular Hg, PHg, is, depending
on aerosol diameter and mass, deposited at intermediate distances (Schroeder & Munthe, 1998).
It has also been shown that in the atmosphere, gaseous elementary mercury (GEM) is rapidly
oxidized to reactive gaseous mercury (RGM), which is thought to be composed of HgCl2
(Muresan, Cossa, Richard, & Burban, 2007). In Table 2.1, different mercury compounds and their
abbreviations are presented.
TABLE 2.1 Mercury compounds (He, Savelli, Graham, Woo, & Kleiman, 2007; Muresan, Cossa, Richard, & Burban, 2007).
Hg compound
Abbreviation
Total gaseous mercury
TGM
TGM = GEM + RGM
Gaseous elemental mercury
GEM
Hg0
Reactive gaseous mercury
RGM
HgII
Particulate mercury
PHg
PHg = THg - DHg
Total mercury (sum of all Hg species)
THg
Dissolved mercury
DHg
Reactive mercury
RHg
Monomethyl mercury
MMHg
Dissolved gaseous mercury
DGM
5
Hg0
2.5 PREVIOUS STUDIES
In a previous study, undertaken in 2003/2004, the distribution and speciation of mercury in air,
rain and surface waters was measured. The location studied was the artificial tropical lake PetitSaut in French Guiana. The results showed an average flux of 12±2 pmol total gaseous mercury
(TGM) m-3. 98 percent of this total gaseous mercury (TGM) was gaseous elemental mercury
(GEM). Total mercury (THg) was found in higher concentrations during late dry season,
compared to lower concentrations in wet season. Concentrations of 3.4±1.2 pmol L-1 of
dissolved THg were found in the surface waters of the reservoir. Variations in concentrations
during the day and night were due to photo-induced dissolved gaseous mercury (DGM)
production, through reactions of GEM with O3, H2O2, OH˙, (60 fmol L-1 h-1). This DGM
production was connected to oxidation and reduction cycles (> 100 fmol L-1) lasting for in
between minutes to hours. The study also presented that up to 75 percent of the invasive flux of
mercury follows the rain pathway (Muresan, Cossa, Richard, & Burban, 2007).
It has been shown that the distribution of GEM demonstrated high concentrations at dawn and
low concentrations in the evening, i.e. a day-and night cycle (Muresan, Cossa, Richard, & Burban,
2007). This daily variation was also established in a study performed in the Mediterranean Sea
(Fantozzi, Ferrara, Frontini, & Dini, 2007). In this study it was also concluded that the flux of
mercury from sea surfaces to the atmosphere were important in the biogeochemical cycle and
that variations in DGM over the day follows the solar radiation intensity. Strong winds increase
mercury evasion, as do mixing surface waters, thereby decreasing DGM levels. There is a
decrease of the exchange of gaseous mercury between the sea surface and atmosphere in the
evenings, due to low wind speeds, resulting in higher mercury concentrations close to the surface.
It was also observed that dissolved organic matter increases the photo-induced reduction of
mercury and that DGM concentrations are lower in the winter as a result of lower temperatures
and better mixing of surface layers, where photochemical reactions occur. The following factors
were identified as limiting for DGM formation; intensity of light radiation (promoting the
mercury reduction), HgII concentration (DGM is produced when HgII is reduced) and the
presence of a special fraction of organic matter that absorbs light radiation (Fantozzi, Ferrara,
Frontini, & Dini, 2007). That mercury flux is strongly correlated with light-radiation was also
concluded in a study performed in Sweden (Xinbin, Sommar, Gårdfeldt, & Lindqvist, 2001).
3 METHODOLOGY
The property of mercury to easily form amalgams together with noble metals, such as gold, silver,
platinum and lead, is taken advantage of when samples containing mercury are pre-concentrated
before determination (Schroeder & Munthe, 1998; Nationalencyklopedin, 2008).
Within this project the analysis was limited to inorganic mercury only due to the short time at
hand. The compounds of mercury intended to be measured in the project, at the different
locations are found in Table 3.1. Due to contaminated hydrochloric acid and alternation of the
method only the two species DGM and THg were analysed however.
6
TABLE 3.1 Types of mercury to be analysed at the different locations (L. Jinlan, personal communication, April 8, 2008).
Type
Abbreviation
Type
Abbreviation
Total Mercury
THg
Dissolved Gas Mercury
DGM
Dissolved Mercury
DHg
Reactive Mercury
RHg
Particulate
Mercury1
1Particulate
mercury was calculated by the formula PHg=THg-DHg
PHg
All of the samples will be analysed according to Method 1631, Revision E: Mercury in Water by
Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry (EPA, 2002). An
overview of the bubbler, purge and trap, cold vapour atomic fluorescence spectrometer (CVAFS)
system can be found in Figure 3.1 whereas a more detailed description of the analysis is found in
section 3.2 below..
FIGURE 3.1 Schematic diagram of the bubbler, purge and trap, cold vapour atomic fluorescence spectrometer (CVAFS) system.
Figure taken from Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic
Fluorescence Spectrometry (EPA, 2002).
3.1 THEORY
It was expected that samples analysed from the two lakes would not contain high mercury
concentrations compared to average mercury concentrations previously measured, i.e. the
mercury concentration in the samples was not expected to be more than the average
concentration in the Atlantic ocean of 0.5 to 3 ng/L. The wastewater was however expected to
be more polluted and therefore contain a higher mercury concentration.
3.1.1 METHOD USED
A brief summary of the EPA method1631 is found below, for the full description please read
Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor
Atomic Fluorescence Spectrometry, EPA, August 2002.
7
Sampling equipment cleaning
New glass bottles are cleaned by heating to 65–75 °C in 4 N HCl for at least 48 h. The bottles are
cooled, rinsed three times with reagent water, and filled with reagent water containing 1% (v/v)
HCl. These bottles are capped and placed in a clean oven at 60-70°C overnight. After cooling,
they are rinsed three more times with reagent water, filled with reagent water containing 0.4%
(v/v) HCl, and placed in a mercury-free clean bench until the outside surfaces are dry. The
bottles are tightly capped, double bagged in new polyethylene zip-type bags until needed, and
stored in plastic boxes until use.
Collection
For analysis of DGM, a sample of 600 mL is collected to a clean glass bottle. Immediately after
collection the sample is transferred into an extensively cleaned glass bubbler, and purged with
mercury-free nitrogen gas with a flow rate of 300mL/min for 30 min. This traps the elemental
mercury in the sample on to a gold trap.
Chemicals
For the standard solutions and analysis the following chemicals, acids and gases were used; ten
chloride dehydrate, hydroxyl ammonium chloride, brome chloride, mercury, nitric acid,
hydrochloric acid, nitrogen gas and argon gas. All of the chemicals used in the experiments were
supplied by 绿茵(Luyin), China.
3.2 ANALYSIS
All of the analyses were done in a laboratory at Xiamen University. Analysis of DGM should be
done at the place of sampling directly. Samples done in this report were however brought back to
the laboratory since lake Furong, at the campus of Xiamen University, the lake in the Nanputuo
temple, connected to campus and the wastewater station on campus grounds all are situated only
a few minutes walk away from the laboratory.
The samples were stored in a bucket with ice and protected against the sun radiation. The reason
for protecting the samples from sun radiation is that the mercury in its oxidised form, HgII will be
reduced to elementary mercury, Hg0, when exposed to sun radiation. Soda lime was used in order
to remove water vapour and carbon dioxide before the gold trap. This soda lime was used three
to four times before its colour darkened and it was replaced with new soda lime.
FIGURE 3.2 Soda lime used in the sampling. (Photo: Caroline Säfström)
8
Analysis 1 – performed 2008-06-19
Sample and performance Analysis 1
In analysis 1, rainwater collected on 2008-06-18 was analysed with the machine AF610B, Rayleigh
with a detection limit of 5 ng/L. Due to malfunctioning of the VM-10 machine in analysis 1, the
analysis method was altered. A standard curve, with the five concentrations [0 0.04 0.12 0.24
0.48 ng/L], had to be prepared by hand and was used for the analysis.
Results Analysis 1
TABLE 3.2 Results from analysis 1.
THg (ng/L)
Rainwater
0.11
In the analysis of the rainwater, the points on the standard curve could not be fitted to a linear
curve and the result was therefore not validated. The concentration that was measured with the
nonlinear standard curve was that the rainwater contained 0.11 ng THg/L, which is below
detection limit for the method used.
Analysis 2 – performed 2008-06-24 and 2008-06-25
Sample and performance Analysis 2
Samples for the second analysis were collected on 2008-06-23 from the Furong lake, located in
Xiamen University campus area. Samples were taken from the lake, which had a temperature of
37°C, 10 cm below the surface at 3:30 pm and were then put in a bucket with ice and brought
straight to the laboratory.
Analysis of the DGM was performed the same day with a VM-10, Rayleigh, detection limit
0.0001 ng Hg/L, connected to the AF610B, Rayleigh. Since the VM-10 was used, only one
concentration of mercury was needed for the standard curve. This was prepared by adding 5 μL
of mercury vapour with a syringe to a gold trap at a known temperature; this temperature is then
put in to the AF610B machine, which created a standard curve from this one concentration. The
analysis of the samples was performed according to EPA method 1631.
Results Analysis 2
TABLE 3.3 Results from analysis 2. (-) this type of mercury was not analysed for the sample, (/) indicates the results from
analyse one and two performed on the same sample.
THg
DGM
Blank
0.86/12.5
0.81
Acid
31
(ng/L)
-(ng/L)
The DGM for lake Furong the DGM was 0.81 ng/L (one sample was used in the analysis). To
analyse THg, three samples were taken on the blank sample in order to make sure that there was
no contamination of mercury in the laboratory. The following concentrations of THg were
9
measured in the non-filtered blank sample; 0.17, 2.8 and -0.38 ng/L (average 0.86 ng/L) and for
the filtered sample the result was the concentrations -6.6 and -0.57 ng/L (average -3.6 ng/L).
Due to the negative values and the large inner variance between the samples yet another analysis
was performed on the non-filtered blank sample collected from the lake, from which another
three samples were used in the analysis. The results from the second analysis of the same sample,
blank, non-filtered, resulted in the following concentrations; 19, 9.2 and 9.3 ng/L (average 12.5
ng/L). These concentrations are much higher than the expected < 0.05 ng/L to be found in the
blank sample and it was therefore expected that the blank sample had been contaminated.
In order to find out the source of contamination, the concentrations of mercury in the
hydrochloric acid was tested. Three samples were taken, each 25 ml, and analysed according to
the EPA method 1631. This resulted in the following concentrations; 36, 46 and 12 ng/L
(average 31 ng/L). The concentration of mercury in the hydrochloric acid should be less than
0.05 ng/L but concentrations measured were 60 times higher than that and it was therefore
concluded that the hydrochloric acid was the source of contamination. Since the acid has been
used in all of the solutions added to the samples in analysis 1 and 2, the results gained are not
valid and new solutions needed to be prepared with a non contaminated hydrochloric acid. New
samples from lake Furong also needed to be taken and new analyses performed.
FIGURE 3.3 Lake Furong at the campus of Xiamen University, Xiamen. (Photo: Caroline Säfström)
Analysis 3 – performed 2008-06-27
Sample and performance Analysis 3
It was not possible to obtain a new hydrochloric acid within the short time frame at hand and the
method used for sampling and preparing the water-samples was therefore altered. As a result of
the alteration in the method, for the following analyses only DGM and THg were analysed since
hydrochloric acid was needed to measure the other types of inorganic mercury species.
Two water samples, both 1 litre, were collected in the same way as before, i.e. 10 cm below the
surface in lake Furong, then brought to laboratory where the sample was put in bubblers, 4 x 200
mL, that were connected in a line. Nitrogen gas was bubbled through the sample for 30 minutes
in order to concentrate the mercury on the gold trap. After that the gold trap was heated to
10
600°C in the VM-10 and then finally analysed in the AF610B where the sampling time used was
35 seconds and analysing time 35 seconds and the argon gas flow was 500 mL/min. This gives
the concentration of DGM in the water.
In order to find out which mercury concentration present above the surface of the lake a flow
meter (CD-1A, MC) with connected soda lime and gold trap was used. The air samples were
taken 15 cm above sea level. A flow of 0.5 L/min was used and sampling time was 20 minutes, i.e.
for each gold trap 10 L air was used. Particular mercury is also present in the air but normally at a
concentration of less than 0.5%, therefore the approximation was done that all mercury analysed
was THg. Three air samples were taken, each of 10 L. The first one was done with out using soda
lime to see if there would be any difference in concentration to the other two samples where soda
lime was being used.
FIGURE 3.4 Flow meter used for the air sampling. (Photo: Caroline Säfström)
Blanks were filled and analysed in the laboratory in order to make sure that the bubblers used not
were contaminated, no blank was filled at site by lake Furong due to that not enough bubblers
were available in the laboratory.
The time of sampling was 2:50 pm with cloudy weather and a water temperature of 29.5°C.
Results Analysis 3
TABLE 3.4 Results from analysis 3. (-) this type of mercury was not analysed for the sample.
THg (ng/L)
DGM (ng/L)
Average (ng/L)
Blank 1
-
0.12
0.067
Blank 2
-
0.013
Water 1 (lake Furong)
-
0.057
Water 2 (lake Furong)
-
0.020
Air 1 (lake Furong)
0.0017
-
Air 2 (lake Furong)
0.0054
-
Air 3 (lake Furong)
0.0053
-
0.039
0.0054
It can be noted in the results that when no soda lime was used during sampling, a lower
concentration of THg was measured in the following analysis.
11
Analysis 4 – performed 2008-06-30
Sample and performance Analysis 4
Since a stable value for the blank samples was not obtained in analysis 3 it was decided to
continue the sampling from lake Furong until this was achieved. Samples for analysis 4 were
collected on Sunday 2008-06-29 and analysed the same day. Sampling of two water samples and
two air samples were done in the same way as in analysis 3 and were performed at 2 pm. At the
time of sampling the water temperature was 32°C and the water had a pH of 8.97. Two blanks
were also done in the laboratory in order to trace possible contamination of the bubblers.
Results Analysis 4
TABLE 3.5 Results from analysis 4. (-) this type of mercury was not analysed for the sample.
THg (ng/L)
DGM (ng/L)
Average (ng/L)
Blank 1
-
0.12
0.13
Blank 2
-
0.13
Water 1 (lake Furong)
-
0.056
Water 2 (lake Furong)
-
0.093
Air 1 (lake Furong)
0.083
-
Air 2 (lake Furong)
0.023
-
0.075
0.053
Analysis 5 – performed 2008-07-01
Sample and performance Analysis 5
In analysis 5, water samples from lake Furong collected in the afternoon the day before were
analysed. At the time of collecting the samples the temperature in the water was 35°C and pH in
the water 9.01. Two water samples, 1 L each, and two air samples of 10 L were taken.
In the previous analysis the variation between the blanks has been large. A reason for this could
be that different gold traps have been used and that this could affect the results. This aspect was
considered in analysis 5 where the same gold trap was used for two blanks and two water samples.
Due to that two air samples are taken at the same time it is however not possible to use the same
gold trap for the air samples. The two water samples, where the same gold trap was used, were
collected on the day of the analysis. This time from a lake in the Nanputuo temple, five minutes
walk away from the laboratory at Xiamen University. The time of sampling was 2:15 pm, the
water temperature was 26°C, and pH in the water 6.51, the procedure of sampling was done in
the same way as in analysis 4.
12
FIGURE 3.5 Sampling at a lake in Nanputuo temple 2008-07-01. (Photo: Caroline Säfström)
In the purpose of controlling the use of the same gold trap but also to control the contamination
of the air inside the laboratory two air samples were taken inside the laboratory and two were
taken of the outside air. All of the air samples were collected for 20 minutes with a flow of 0.5
L/min.
In analysis 5 the used volume of water for the analysis was diminished from 800 mL to 600 mL
due to limited access to bubblers in the laboratory.
Results Analysis 5
TABLE 3.6 Results from analysis 5. (-) this type of mercury was not analysed for the sample.
THg (ng/L)
DGM (ng/L)
Average (ng/L)
Blank 1
-
0.18
0.27
Blank 2
-
0.41
Blank 3
-
0.21
Water 1 (lake Furong)
-
0.18
Water 2 (lake Furong)
-
0.26
Water 1 (Nanputuo temple)
-
0.21
Water 2 (Nanputuo temple)
-
0.21
Air 1 (lake Furong)
0.0036
-
Air 2 (lake Furong)
0.014
-
Air 1 (inside laboratory)
0.037
-
Air 2 (inside laboratory)
0.045
-
Air 1 (outdoors)
0.016
-
Air 2 (outdoors)
0.016
-
0.22
0.21
0.0088
0.041
0.016
Due to the variance of two blanks analysed a third blank was analysed. The two air samples from
inside the lab had THg concentrations of 0.037 and 0.045 ng/L and the two air samples from the
outdoor air both had a THg concentration of 0.016 ng/L. This shows that the air inside the
laboratory has a THg concentration 2.6 times higher than the air outside, which could increase
the contamination of mercury to the samples when handled in the laboratory.
13
FIGURE 3.6 The samples were protected against sun radiation throughout the analysis in order to prevent reduction of Hg(II) to
Hg(0). (Photo: Caroline Säfström)
Analysis 6 – performed 2008-07-02
Sample and performance Analysis 6
From analysis 5 it was evident that if the same gold trap is used, a more stable value is obtained.
Since two air samples are taken from one location at the same time it is not possible to use the
same gold trap for the air samples. For the water samples, however, the same gold trap has been
used for both samples. This gold trap is the same one that has been used when analyzing the two
blanks.
In analysis 6 sampling was continued from Nanputuo temple. Two water samples were taken
from the same lake inside the temple as in analysis 5, as well as two air samples with the same
method used in the previous analyses. The two air samples were taken approximately 1.50 m
above the water surface due to limited space to place the flow meter. Time of sampling was 3:20
pm, the temperature in the water was 26°C and pH was 6.48. When the two blanks were
performed in the morning, the first one had a concentration over the wanted value of 0.1 ng/L
and the gold trap was therefore switched for another one, which is the reason why three blanks
were performed.
Results Analysis 6
TABLE 3.7 Results from analysis 6. (-) this type of mercury was not analysed for the sample.
THg (ng/L)
DGM (ng/L)
Average (ng/L)
Blank 1
-
0.31
0.29
Blank 2
-
0.27
Blank 3
-
0.30
Water 1(Nanputuo temple)
-
0.19
Water 2 (Nanputuo temple)
-
0.13
Air 1 (Nanputuo temple)
0.014
-
Air 2 (Nanputuo temple)
0.016
-
14
0.16
0.015
Analysis 7 – performed 2008-07-03
Sample and performance Analysis 7
In analysis 7 samples were collected from a wastewater treatment station on the edge of Xiamen
University campus. The sampling was not possible to perform in the same way as in the previous
analyses due to that it was not possible to get down to the wastewater surface. A bucket was
therefore used to gather wastewater with and then pored into two one litre glass bottles. The two
air samples had to be taken at ground level, which was approximately seven meters above the
wastewater surface, which could result in that a lower mercury concentration is measured than
actually present just above the wastewater surface.
FIGURE 3.7 Sampling from wastewater treatment station in Xiamen University 2008-07-03. (Photo: Caroline Säfström)
At the time of sampling, 15:10 pm, the wastewater had a temperature of 28°C and the pH was
6.62. When water sample number two was analysed it was noticed that the soda lime became pink
discoloured towards a blue dark purple colour. Most likely this was due to some reaction with
some substance present in the wastewater.
Results Analysis 7
TABLE 3.8 Results from analysis 7. (-) this type of mercury was not analysed for the sample.
THg (ng/L)
DGM (ng/L)
Average (ng/L)
Blank 1
-
0.069
0.052
Blank 2
-
0.034
Water 1 (wastewater treatment station)
-
0.41
Water 2 (wastewater treatment station)
-
0.21
Air 1 (wastewater treatment station)
0.012
-
Air 2 (wastewater treatment station)
0.014
-
0.31
0.013
Analysis 8 – performed 2008-07-05
Sample and performance Analysis 8
Two air samples were taken in analysis 8 from the conference room, number B105, Ocean
building, where the results from this report were to be presented in the following week. Time of
sampling was 9.30 am.
15
Results Analysis 8
TABLE 3.9 Results from analysis 8. (-) this type of mercury was not analysed for the sample.
THg (ng/L)
DGM (ng/L)
Average (ng/L)
Air 1 (conference room)
0.0020
-
0.0022
Air 2 (conference room)
0.0024
-
4 RESULTS
Concentrations of mercury in Furong lake can be found in Figure 4.1, below.
LAKE FURONG
Hg conc. (ng/L)
0.3
0.25
0.2
0.15
0.1
0.05
0
Analysis 3
Analysis 4
Analysis 5
Blank 1 (DGM)
0.12
0.12
0.18
Blank 2 (DGM)
0.013
0.13
0.21
Water 1 (DGM)
0.057
0.056
0.18
0.02
0.093
0.26
Air 1 (THg)
0.0054
0.083
0.0036
Air 2 (THg)
0.0053
0.023
0.014
Water 2 (DGM)
FIGURE 4.1 Results form the analysis of mercury in Furong lake. (blank) water sample done in laboratory to trace contamination,
(water) water sample taken at the lake, (air) air sample taken at the lake.
The mercury levels in the air analysed from Furong lake have a 2 to 83 times higher mercury
concentration than the average air concentration of 0.001 to 0.002 ng/L whereas the water
samples have mercury concentrations below the average ocean values from the literature of 0.5 to
3 ng/L. The blanks are all close to wanted value of no more than 0.1 ng/L apart from in analysis
5 where the values are somewhat higher.
Due to that four blanks analysed in the laboratory shows a higher concentration of mercury than
the samples collected in the lakes it is likely that the samples have been contaminated and it is
therefore hard to determine if the mercury concentration measured is due to contamination or
actual present concentrations.
16
OTHER SAMPLES I
Hg conc. (ng/L)
40
30
20
10
0
Sample 1
HCl (THg)
Blank (THg)
31
0.86
12.5
Sample 2
FIGURE 4.2 Results form the analysis of mercury in the hydrochloric acid used in the laboratory as well as in two blanks.
As can be seen in Figure 4.2 the hydrochloric acid that is used for all solutions to prepare the
samples have a high concentration, 31 ng/L, of mercury. The results from analysis 1 and 2 are
higher than what was expected to be found in rainwater and especially in a blank sample. The
reason for this is that the hydrochloric acid has contaminated the samples in analysis 1 and 2.
There is also a big variance between the two samples that were done in the same way for the
blank in analysis 2. This could be due to that the gold traps had not been cleaned efficiently
enough before starting the analysis or that the standard mercury vapour used contaminated the
first sample analysed thereafter.
NANPUTUO TEMPLE
0.35
Hg conc. (ng/L)
0.3
0.25
0.2
0.15
0.1
0.05
0
Analysis 5
Analysis 6
Blank 1 (DGM)
0.18
0.3
Blank 2 (DGM)
0.21
0.27
Water 1 (DGM)
0.21
0.19
Water 2 (DGM)
0.21
0.13
Air 1 (THg)
0.014
Air 2 (THg)
0.016
FIGURE 4.3 Results form the analysis of mercury in a lake inside Nanputuo temple. (blank) water sample done in laboratory to
trace contamination, (water) water sample taken at the lake, (air) air sample taken at the lake.
17
In Figure 4.3, the mercury concentrations analysed from Nanputuo temple can be found. The
concentration measured in the air of the Nanputuo temple is 7 to 16 times higher than the
average air concentration whereas the concentration in the water is lower than the average. In the
same way as for the analyses carried out for Furong lake, the blank values for Nanpotou temple
are higher than the concentrations measured in the water for all water samples but one. This once
again raises the question whether the mercury measured actually comes from the site of sampling
or from contamination in the laboratory.
It can be seen in Figure 4.4 the concentration of mercury in the wastewater is not considerably
higher than what was found in the two lakes. The value in water sample one is almost twice that
of the concentration found in water sample two, suggesting that water sample one can have been
contaminated. The air samples have mercury concentrations of 6 to 14 times higher than the
average whereas all the water samples have mercury concentrations below average.
WASTEWATER
0.45
Hg conc. (ng/L)
0.35
0.25
0.15
0.05
-0.05
Analysis 7
Blank 1
(DGM)
Blank 2
(DGM)
Water 1
(DGM)
Water 2
(DGM)
0.069
0.034
0.41
0.21
Air 1 (THg) Air 2 (THg)
0.012
0.014
FIGURE 4.4 Results form the analysis of mercury in wastewater. (blank) water sample done in laboratory to trace contamination,
(water) water sample taken at the lake, (air) air sample taken at the lake.
Mercury was also analysed in rainwater and air inside the laboratory, outdoors and in a
conference room, see Figure 4.5. This gave the result that the rainwater contains mercury at levels
lower than the average whereas the air inside the conference room is at the average level for air.
The air outside the laboratory is 8 to 16 times higher than average and inside the laboratory the
air contains mercury at 19 to 45 higher concentrations than the average air.
18
OTHER SAMPLES II
Hg conc.(ng/L)
0.12
0.1
0.08
0.06
0.04
0.02
0
Rainwater (THg)
Sample 1
Sample 2
0.11
Air inside lab (THg) Air outdoors (THg) Conf. room (THg)
0.037
0.016
0.002
0.045
0.016
0.0024
FIGURE 4.5 Results form the analysis of mercury in other samples II. (rainwater) rainwater that was collected in a bucket, (air
inside lab) air sample taken inside the laboratory where the analyses were performed, (air outdoors) air sample taken outside the
laboratory on a balcony, (conf. room) air sample taken in a conference room in the Ocean building at Xiamen University.
5 DISCUSSION
Mercury concentrations in the two lakes and wastewater tested are all lower than the average
ocean average concentration and these neither the lakes nor the wastewater is therefore not
considered to be polluted by mercury.
The air samples on the other hand all have a higher concentration than the average apart from
inside the conference room. It is reasonable that the air inside the laboratory does contain a
higher level of mercury due to contamination. The concentration of mercury inside the
laboratory had also been measured one and two months before the project started and the values
had been at the same concentrations as in analysis 5. That the air in the sampling places has
higher mercury concentrations than average indicates that the water bodies function as mercury
sources and that there is a flux of mercury from the water surface to the air. This flux is higher
when the temperature is high which corresponds well with that the air samples have been taken
during the warmest time of the day. There is also mercury deposition from surrounding air and it
should be mentioned that there is a power plant situated on the other side of the bay that could
be a contribution to the higher mercury concentration in the air.
It is notable that in the analyses concentrations in the blanks are many times higher than the
mercury concentrations in the water samples. This indicates that there is a risk that the water
samples have been contaminated when they have been transferred to the bubblers. There is also a
variance within the blanks performed. When the same gold trap have been used the variance
seems to be smaller, however more analyses are needed to establish this.
When the difference between using soda lime and not was tested, the results showed that when
soda lime is used, a higher THg concentration is detected. This could be because there is less
19
interference from carbon dioxide and water vapour on the gold trap. Soda lime should therefore,
as recommended in the method the experiments have been carried out from, always be used.
In the pond inside the Nanputuo temple there were considerable amounts of fish present which
does correspond well with the low concentration of mercury found. Partly because of mercury
levels were to be very high the fish would not survive but also because of if some mercury would
be present it could accumulate in the fish.
The concentration of mercury measured in the wastewater was lower than expected. A reason for
this could be that it was discovered that the wastewater station where the water samples were
taken from receive not only wastewater but also water from the ponds and lakes in Putuo temple.
This dilution of the wastewater would explain the lower concentration that was measured.
5.1 IMPROVEMENTS
The following improvements are suggestions that can be done in order to gain more stable and
reliable results in the continued experiments;
-
Use of one analysis gold trap for all samples, including air samples, to which the mercury is
transferred from different sample gold traps used in order to diminish the variation between
the samples..
-
Use of super-purified hydrochloric acid to prevent contamination.
-
Analysis of DGM directly at the time and place of sampling to decrease the effect from i.e.
solar radiation to the sample.
6 CONCLUSIONS
The following concentrations of mercury were found at the different locations;
-
In Furong lake, situated inside Xiamen university campus area, DGM concentrations in the
water reach from 0.02 to 0.3 ng/L and in the air THg concentrations were from 0.004 to 0.08
ng/L.
-
For the pond inside Nanputuo temple water concentrations of DGM were 0.1 to 0.2 ng/L
and air concentration of THg from 0.01 to 0.02 ng/L.
-
The wastewater contained DGM of 0.2 to 0.4 ng/L and the air sample at the wastewater
station 0.01 ng THg/L.
-
The rainwater had a mercury concentration of 0.1 ng/L and the air inside a conference room
in the Ocean building at Xiamen University contained 0.002 ng THg/L.
It is indicated from the results that the lakes, wastewater, rainwater and conference room air are
not polluted by mercury when compared to average values found in the literature. The water
bodies does however serve as sources of mercury to the air since mercury concentrations
measured in the air above the water bodies all were higher than the average value expected to be
found in the air. There are although also other sources adding mercury to the air in the nearby
area apart from the water bodies, i.e. a power station.
20
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gaseous mercury concentration in the Mediterranean Sea. Marine Chemistry , 107, 4-12.
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Meili, M., Bishop, K., Bringmark, L., Johansson, K., Munthe, J., Sverdrup, H., et al. (2003). Critical levels of
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Schroeder, W. H., Munthe, J., & Lindqvist, O. (1989). Cycling of mercury between water, air, and soil compartments
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21
7 APPENDICES
As a part of the International Summer Water Resources Research School an evaluation is
expected from the students. This Appendix contains that evaluation.
7.1 EVALUATION
The following aspects have been considered in the evaluation; laboratory work, team work, the
writing of the report, the university and the total impression of the course.
7.1.1 LABORATORY WORK
All of the laboratory work has been performed together with one Chinese laboratory assistant
and two Chinese students. The language used in the laboratory has been English at almost all
times. The work in the laboratory has been shared equally by all participants and has provided a
good knowledge of methods of how to analyse inorganic mercury.
During the laboratory work the conditions have changed due to malfunctioning of machines or
values that have not been in line with the expected concentrations. This has been handled in an
excellent way by finding alternative methods and everyone involved in the project have been
optimistically flexible in this matter.
7.1.2 TEAM WORK AND REPORT
The first two days there were some language difficulties but after this starting period there have
been no problems communicating in the laboratory. The team work in the laboratory has been
excellent whereas in the preparation of abstract and PowerPoint presentation the work load has
mainly been on the Swedish student. This has been in part to ease the work load of the Chinese
students whom were having laboratory experiments still running in the week of the presentation.
7.1.3 XIAMEN UNIVERSITY
During my stay at Xiamen University each individual I have come in contact with have been kind
and helpful. There have never been any problems in getting access to computers, sport activities
or getting help with administrative questions. This helpfulness has come not only from the
people involved in SRS but also from students at the University and strangers in the street.
7.1.4 IN TOTAL
To participate in SRS 2008 have provided an excellent opportunity to gain further laboratory
knowledge within a new field of science as well as an understanding of a different way of both
studies and culture. I am very satisfied with how the laboratory work has preceded; even though
we did not at all times have access to enough laboratory equipment. The outcome of the course is
a result of the good cooperation with the Chinese team of the project.
22