How Much Arsenic Do We Eat?
Analytical chemists make light work in
tracking potentially harmful chemicals
Julian Tyson
Department of Chemistry
UMass Amherst
Analytical chemists provide information about
the chemical composition of materials. So
that a decision can be taken.
How do analytical chemists make light work
in tracking potentially harmful chemicals?
Interaction of light with materials.
Light is a wave and is a form of
energy. The energy of light is
inversely related to its wavelength.
Short wavelength: high energy.
Long wavelength: low energy
Summary of where we are now.
Color of objects is due to the absorption of light.
Absorption is due to the molecules.
The wavelengths of the light absorbed tell us
something about which chemicals are present.
Amount of light absorbed depends on the number of
molecules in the light beam, so
The extent of the absorption tells us something about
how much of a chemical is present.
Analytical chemists use the interaction of light with with
molecules that contain arsenic to measure the arsenic in
relevant materials.
So how does arsenic get into relevant materials?
Arsenic occurs in nature. It is about the 40th most abundant
element on the planet. Geological processes have spread it
around. We’ve extracted it from ores, made useful compounds
and spread them around.
Open ocean water:
River and surface water:
about 1 - 4 ppb
about 0.1 - 1 ppb
The arsenic in the environment story
Orpiment As2S3
Arsenic trioxide As2O3
Realgar As4S4
Arsenic As
Ground water: a major problem
around the world. Especially in
SE Asia (Bangladesh and West
Bengal, India)
Concentrations: 0.1 – 1000 ppb.
US EPA limit is 10 ppb
Concentrations in soil are about 2 mg kg-1. But there are
considerable variations and there’s a legacy of previous
agricultural practice to deal with.
Amounts. Weight:
1 kilogram (kg) = 2.2 lb = 1,000 grams (g)
1 milligram (mg) = one-thousandth of a gram
1 microgram (µg) = one-millionth of a gram.
A grain of salt weighs 2 mg
(the official grain is 65 mg)
Amounts. Volume:
liter (L) = 0.26 gallon (US) = 1,000 milliliters (mL)
1 milliliter (mL) = one-thousandth of a liter
1 microliter (µL) = one-millionth of a liter
A drop (of water) is about 50 µL
A bathtub contains about 230 L
Concentrations in solids: mass per mass
1 part per million (ppm) is 1 milligram in 1 kilogram i.e. 1 mg/kg
or 1 microgram in 1 gram i.e. 1 µg/g
Scientist sometimes write this as 1 µg g-1
A part per billion (ppb) is 1 µg kg-1
Concentrations in liquids: mass per volume
1 part per million (ppm) is 1 milligram in 1 liter i.e. 1 mg/L
or 1 microgram in 1 mL i.e. 1 µg/mL
Scientist sometimes write this as 1 µg mL-1
A part per billion (ppb) is 1 µg L-1
1000 ppb = 1 ppm
How to make a 10 pbb solution
One grain weighs 65 mg
(2.5 mm cube of As2O3)
76% by weight is As
49 mg
21 bathtubs contain
21 x 233 L = 4,900 L
1 grain in 21 bathtubs = 10 ppb
The US EPA limit for arsenic
in drinking water
Arsenic speciation
There are a lot of different arsenic compounds in the environment.
Inorganic
Organic
Arsenic bonded to oxygen
and/or sulfur or hydrogen.
Arsenic bonded to carbon
and/or oxygen or hydrogen
Methylated arsenate
As2O5
As2O3
AsH3
H3AsO4 arsenate
H3AsO3 arsenite
arsine
CH3AsO(OH)2
MMA
(CH3)2As(O)OH DMA
Arsenobetaine, arsenocholine
Some formulae for the chemists in the audience.
arsenite
arsenate
monomethylarsonate
cacodylate
dimethylarsinate
trimethylarsine oxide
More formulae for the chemists in the audience.
trimethylarsine oxide
tetramethylarsonium
Yet more formulae for the chemists in the audience.
TETRA
arsenobetaine
Seafood arsenic
arsenocholine
Not all arsenic compounds are very toxic
OK - all chemicals are toxic: it all depends on the dose and
how you interact with them.
Some arsenic compounds are “non-toxic.”
arsenobetaine and arsenocholine and arsenosugars
seafood arsenic
Some arsenic compounds are toxic
Acute lethal dose of As2O3 is about 100 mg for a 70-kg adult.
About 2 grains or a 3 mm cube.
Some arsenic compounds are sort of non-toxic
Monomethyl and dimethyl arsenates
The adverse health effect of concern is cancer.
How does arsenic get into our food? Plants take up arsenic
compounds from the soil. Legacy of previous applications.
How arsenic gets into crops
How do we know whether food
and drink contains potentially
harmful forms of arsenic?
us.
Ask the analytical chemists. They tell
• Seafood contains non-toxic forms
• Drinking water contains toxic, inorganic forms
• Food contains toxic (inorganic) and sort-of toxic forms
(mono- and di- methylated).
Approach: Measure total arsenic and assume it is all toxic.
If less than guideline value: no problem
If more than guideline value: more analysis needed
How much arsenic is considered safe?
How much inorganic arsenic is considered safe?
Food: No US guideline value.
Drinking water: US EPA 10 µg L-1 (ppb)
Joint FAO/WHO expert committee on food additives,
seventy-second meeting, Rome, 16–25 February 2010,
summary and conclusions Issued 16th March 2010
http://www.who.int/foodsafety/chem/summary72_rev.pdf
The limit for dietary inorganic arsenic exposure is:
3.0 µg per kg body weight per day
How much inorganic arsenic is considered safe?
Dietary: 3.0 µg per kg body weight per day.
Developmental
stage
Weight lbs
1 lb = 0.45 kg
Tolerable daily
intake µg
Newborn
7
9
1-year-old
22
30
5-year-old
42
57
teenager
140 (m) 117 (f)
191 (m) 160 (f)
young adult
155 (m) 127 (f)
211 (m) 173 (f)
Adult (US average)
191 (m) 164 (f)
260 (m) 224 (f)
300
409
your call
> 400
football player
overweight
Acute lethal dose (adult) 100 mg
How much inorganic arsenic do we actually eat?
Food: Ask the analytical chemists.
Developmental
stage
Weight lbs
1 lb = 0.45 kg
Tolerable daily
intake µg
Newborn
7
9
1-year-old
22
30
5-year-old
42
57
teenager
140 (m) 117 (f)
191 (m) 160 (f)
young adult
155 (m) 127 (f)
211 (m) 173 (f)
Adult (US average)
191 (m) 164 (f)
260 (m) 224 (f)
300
409
your call
> 400
football player
overweight
Acute lethal dose (adult) 100 mg
A market basket survey of inorganic food in rice
Food and Chemical Toxicology 37 (1999) 839-846
Examined 40 commodities expected to deliver 90% of total dietary
inorganic arsenic. Took 4 samples of each. Measured total arsenic
and inorganic arsenic.
Food
Total arsenic
µg kg-1 wet weight
Inorganic arsenic
µg kg-1 wet weight
saltwater finfish
shrimp
2,400
1,900
0.5
2
tuna
rice
chicken
512
303
86
1
74
1
grape juice
beef
peanut butter
58
52
44
9
0.4
5
watermelon
flour
spinach
apple juice
40
39
5
8
9
11
6
3
Environmental Health Perspectives, 2010, 118, 345-350
Probabilistic modeling of dietary arsenic exposure and
dose and evaluation with 2003-2004 NHANES Data
Scientists at US EPA, National Taiwan University, and the
Environmental and Occupational Health Sciences Institute
Inorganic arsenic.
12
11
24
18
17
5
13
Environmental Health Perspectives, 2010, 118, 345-350
Results: Mean total exposure from food is 0.38 µg per kg body
weight per day. 14-times higher than the mean exposure from
drinking water. Exposure from food is 0.05 µg per kg body
weight per day i.e. 1.96 µg per day.
Approximately 10% of exposure from food is
the toxic inorganic form of arsenic.
The average American
weighs 40 kg i.e. 88 lbs.
Calculated exposure from food.
Total arsenic: µg per kg body weight per day
Age
Number
Average
5th
percentile
99th
percentile
0-1
1-2
757
1,068
0.62
0.54
0.05
0.05
2.08
5.06
3 -5
963
0.54
0.03
5.6
6-12
13 -19
2,190
3,576
0.37
0.25
0.02
0.01
4.28
3.58
20 - 49
>50
All
4,221
3,804
16,931
0.33
0.32
0.36
0.01
0.01
0.01
4.12
4.91
4.45
Calculated exposure from food.
Inorganic arsenic: µg per kg body weight per day
Age
Number
Average
5th
percentile
99th
percentile
0-1
1-2
757
1,068
0.23
0.1
0.01
0.01
0.8
0.59
3 -5
963
0.08
0
0.4
6-12
13 -19
2,190
3,576
0.04
0.03
0
0
0.25
0.21
20 - 49
>50
All
4,221
3,804
16, 931
0.03
0.03
0.05
0
0
0
0.28
0.22
0.41
The Schoof report: A market basket survey of inorganic food in rice
Food
Total arsenic
µg kg-1 wet weight
rice
Total Inorganic
arsenic
303
MMA
DMA
Inorganic arsenic
µg kg-1 wet weight
74
I + MMA +
%
DMA
missing
335
218
462
55
62
81
ND
ND
3
ND
61
202
55
123
286
84
44
38
196
97
2
99
198
0
There’s a problem with the Schoof analysis of the rice.
What do other researchers find about arsenic in rice?
Food Additives and Contaminants: Part B, 2009, 2, 112-120
Survey of total arsenic and arsenic speciation in US-produced rice
as a reference point for evaluating change and future trends.
Heitkemper and colleagues at USFDA Cincinnati
The average total content was 210 µg kg-1.
Regardless of total content, inorganic arsenic
rarely exceeded 150 µg kg-1.
Arsenic content in US rice has been relatively
constant over the past 30 years.
All values in µg kg-1 based on dry weight.
Date
1980-81
Location
LA
Total
167
Inorganic
105
% missing*
-9
1980-81
1980-81
1980-81
1980-81
AR
TX
CA
AVE US
184
445#
62
202
79
111
61
90
-11
0
-33
-13
2001-02
AVE US
264
98
-11
*The minus sign means that the sum of I + MMA + DMA > total
#One
sample had over 1000 µg kg-1 total: inorganic 150 µg kg-1
Heitkemper and colleagues at US FDA Cincinnati
Conclusions
“In comparison with inorganic arsenic, much less is
known regarding the toxicity and biotransformation
pathways associated with dietary intake of DMA.
Although generally considered to be less toxic than
inorganic arsenic, more information about the longterm exposure effects of DMA may be necessary to
evaluate fully the risk of rice consumption, given the
high DMA content that has been reported in rice.”
What do other researchers find about arsenic in rice?
Meharg and colleagues at the University of Aberdeen
Arsenic in rice around the world. All values in µg kg-1
Location
Bangladesh
China
Egypt
Average
Total
130
Max total
Average
inorganic
80
Max
inorganic
210
160
No data
380
No data
140
50
330
460
580
France
280
560
No data
No data
India
Italy
70
150
180
330
30
110
70
160
Japan
190
420
No data
No data
Spain
200
820
No data
No data
Meharg and colleagues at the University of Aberdeen
Conclusions
“The modeling outlined here indicates that eating rice at typical
SE Asia consumption rates, or at higher percentile consumption
rates in developed countries, constitutes a significant excess
cancer risk to those populations, well above the targets set by US
EPA and WHO for carcinogenic sources.”
“As cancers caused by chronic exposure to arsenic sources have
a latency of approx. 20 years, the data presented here suggest
that long-term epidemiological studies need to be undertaken to
characterize this risk.”
Researchers call for monitoring of arsenic levels in rice
By Elizabeth Weise, USA TODAY Dec 5, 2011
Proceedings of the National Academy of Sciences of the USA Dec 5th 2011
Rice consumption contributes to arsenic exposure in US
women
Diane Gilbert-Diamond and coworkers at Dartmouth College
“Emerging data indicate that rice consumption may lead to
potentially harmful arsenic exposure.”
“Although inorganic arsenic is thought to be more harmful that
DMA, further epidemiological studies are needed to better
understand the health risks of DMA . . . It is imperative that the
health impact of arsenic exposure through rice consumption be
characterized.”
www.pnas.org/cgi/doi/10/.1073/pnas1109127108
How Much Arsenic Do We Eat?
The question really should be: How much inorganic
arsenic and methylated arsenic do we eat?
Answer: depends on what foods we eat. Rice has a
much higher concentration than any other food.
What sort of rice, where from and how much.
White rice contains less arsenic than brown rice.
Where grown. USA, France, and Spain (max total)
China, Bangladesh and Italy (max inorganic).
Bioavailable? Assume 100%.
So. What about apple juice?
88 samples purchased in Aug and Sept 2011 in CT, NJ, and NY.
There’s no federal limit for
arsenic in juice.
25% of samples exceeded 5 ppb
and 10% exceeded 10 ppb.
Recommended dietary limit is 3
µg per kg body weight per day.
30 - 60 µg for young children.
Need to drink 1.2 – 2.4 L
i.e. 2.5 – 5 pints per day.
Take digital picture with digital camera.