CHEMOSPHERE
REVISION, Manuscript Number: CHEM9786
Title: Assessment of heavy metal pollution in minesoils and phytoaccumulation
in Pingle Manganese mine wasteland, South China
Article Type: Research Paper
Section/Category: Environmental Toxicology and Risk Assessment
General comments
The study presents original data on the total and extractable concentrations of metals
(Mn, Pb, Zn Cu, Cr and Cd) in soils from a manganese mine in Guangxi (China) and in
plants growing on the soils. The subject is within the scope of the journal and focuses
on a type of mining (Mn) to which little attention has been given. However, the
manuscript cannot be published in its present form, for the following reasons:
1. There is a lack of relevant information that would allow interpretation and
discussion of the results, particularly as regards description of the study area
(geological material and types of soil present) and the method of sampling.
2. The number of soil samples collected (12) is clearly not sufficient to represent
1300 ha of wasteland. Studies on mine soils highlight the high heterogeneity of
these types of soils and the need for a large number of samples to achieve
representability.
3. There are serious errors in the interpretation of the results of the study and of
previously published data.
4. The conclusions reached are not supported by the results obtained.
5. Of the 61 bibliographic references given, 24 are published in China in journals
that are not accessible to the majority of the readership of Chemosphere.
6. The text, although generally well written, would benefit from revision by a
native English speaker, preferably a scientist.
The authors could prepare a new version of the study (see specific comments) that
would be subject to a new revision.
Specific comments
Coment
1. Introduction:
 Indicate the significance of RMB yuan and give an approximate
equivalent in a reference currency (for example, dollars).
2. Materials and methods
 Include the relevant information about the geology and the soils in
the zone in a description of the study area………………………
 Indicate the surface area occupied by each of the zones in which the
mine is divided (M, FTD, RTD and R)…………………………
 I think that the number of soil samples collected (12) is clearly not
sufficient to represent 1300 ha of wasteland. Studies on mine soils
highlight the high heterogeneity of these types of soils and the need
for a large number of samples to achieve representability. How
were the sampling sites within each zone and the sampling points
within each site chosen? What is the surface area of the sampling
area? What is the distance between sampling points?....................
 Indicate where and how the plants samples were collected: whether
samples were collected from a single plant or from several plants,
whether the entire plant was sampled or only a part, how many
samples were collected of each species and at each site …...
 Indicate the extraction method used for analysis of total phosphorus
(TP). Indicate the form the results for TP refer to (elemental P,
P2O5, PO43-,…). ……………………………………………………
 The authors do not state whether certified reference materials were
included to check the percentage of recovery in the analysis of total
metals in soils and plants …………………….
 Omit the headings of sub-sections 2.4.1 and 2.4.2
 Include the bibliographic reference for the “Chinese Environmental
Quality Standard for Soils” ………………………………………..
 References are not provided for the analytical methods used .
Results
 The pH of the soil should be rounded to one decimal place
 The intervals of concentration of moderate class TN and OM
should be given in accordance with the Chinese Soil Fertility
Standard (NY/T 391-2000). The reference does not appear in the
reference section
 The authors state that: “All the extractable metal fractions were below
5%, indicating a very low availability to plants”. This is not true as
although the percentage of extractable metals is relatively low, the
amount of bioavailable metal is very high, especially for Cd and Mn.
 In the text, Cd (3.55%) and Cr (0.19%) should read Cd (4.43%) and
Cr (0.23%).
 Li et al, 2006b should be cited as Li et al, 2007 (date of publication of
the journal)
 It is not true that the contamination indices (Pi and I-geo) follow the
Line
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same pattern. Only those obtained for Zn and Cu are comparable.
They are not comparable for Pb or for Cr. The I-geo index for Cd is
not given.
Avoid repetition. It is not necessary to continually remind the
reader what the Pi index is when it is explained in the previous
paragraph.
Delete the sentence “The difference was mainly attributed to the
assessment criteria (natural soil background vs. soil quality standard)
used (see Discussion).”
Replace ND (not detectable) with “< limit of quantification” (e.g. <0.5
mg/kg). Which values were used in the statistical analysis when the
value was ND? This should be explained in the statistical methods.
The concentrations of Cr and Cd reached high levels in plants even
though “ the bioavailability is low in relation to the total Cr”.
The correct reference for Cao, 2001 is Cao and Chi, 2001.
Establish a method of ordering the metals (alphabetical order,
concentration… ). Follow the same order in the text, except with
groups.
Indicate where normal levels of heavy metals are found in plants.
What type of plants does this refer to, what part of the plant, where
the plants are growing…..
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Discussion
 In this section the authors simply present a series of previously
reported studies, without putting into perspective the results
obtained in their own study. They also use vague terms such as
“low” and “high”, without giving numerical values. Furthermore as
most of the studies cited are in Chinese, they cannot be consulted
by many of the readers of Chemosphere.
In the first paragraph, for instance, 4 examples of Pb/Zn, Cu, Sn/Sb
and Mn mines are given, but only data for Cu are provided.
 The authors indicate that the Pi index is widely used, but I
understand that the standard reference values used to calculate them
may vary depending on the particular study in question. What
values were used in the cited studies? Do they coincide with those
used in the present study?
 The authors state that: “The difference of the two assessments lies in
that I-geo linked theoretically all “pollution contribution” to the soil
background value only, not discriminating the natural lithogenic effect
from anthropogenic contribution.” Does the Pi index make this
discrimination? I understand that the I-geo index is more appropriate
for making this discrimination, as it includes background levels of
metals in natural soils in the area, and presumably over a similar
geological substrate.
 All of the phytotoxicity data for metals given in this paragraph must
be revised and compared with those given by other sources. Many
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of the data in the list are taken from different sources, without any
apparent underlying reason for including them. It is not clear
whether the phytotoxic concentrations given correspond to the soil
or the plants, or under what conditions they were obtained. For
example, the authors give the total concentration of Cu in soil as
60-125 mg/kg, (Ross, 1994). However, they give the the phytotoxic
thereshold as the concentration of Mn in plants that are very
tolerant to metals and grown in hydroponic cultures (Paschke et al.,
2005). Although I was unable to consult the paper of Jiang et al.
(2001), I assume that the phytotoxic concentration of Cd given (70150 mg/kg) corresponds to the concentration in Brassica juncea, a
metal tolerant plant that accumulates metals, and that was grown on
soils contaminated with Cd and treated with EDTA (which
increases the solubility of the metal), with the aim of using them as
phytoextractors. Data such as 3-8 mg Cd/kg of soil or 1500-3000
mg Mn /kg soil are commonly given as critical levels for
phytotoxicity (Ross, 1994). Finally, despite the attempt to revise the
phytoxicity values, the results of the present study were not
discussed in this context.
The authors state that: “Conclusively the minesoils basically have a
low metal-toxic potential to higher plants although they were assessed
as heavily contaminated. The diverse mineland flora (over 30 plant
species) and bearing fruit of planted peach trees in the restored area
may support this.”
This cannot be concluded either from the results of the present study
or from discussion of the results of previously published studies. It is
widely accepted that the total concentration of metals in the soil
overestimates the risk of phytotoxicity, but in the present study,
despite the low relative extractability of the metals, the bioavailable
concentration of some metals is sufficiently high to surpass the
thresholds of phytotoxicity. In addition, several studies have shown a
poor correlation between bioavailable metals in soil and the metals
absorbed by plants, as the latter can modify the soil conditions in the
rhizosphere (increasing or decreasing the bioavailability of metals) and
may develop specific physiological strategies for excluding or
accumulating metals depending on the plant species.
This part of the discussion should be shortened as these data were
not provided in the present study. The conclusions reached in this
paragraph are the opposite of the previously mentioned conclusions.
References
 Provide the dates of publication of the journals, along with the
volume and the corresponding pages, not the document available
on-line.
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