Transcript Hazardous Waste Characterization, Generic Cleanup Criteria

Preliminary Findings – Assessment of
Soils and Crops in the Zacatecas Area –
Mexico – July 2002
Mercury Task Force Meeting and Public
Workshop – Zacatecas, Mexico
Commission for Environmental Cooperation
Ron Pearson, M.Sc.
BARENCO INC
Ontario, Canada
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Scope of Work
 To undertake a literature review and scoping investigation
related to the environmental impact of historical silver and
gold mining operations in the Zacatecas area on agricultural
activities as well as on ecological and human health.
 As part of the scoping investigation, to undertake a
preliminary sampling program involving the collection of a
limited number of soil and vegetation samples for exploratory
analysis of mercury and other environmental parameters.
 Based on the results of the soil and vegetation sampling
program and on information gathered pertaining to the
potential receptors and exposure pathways, to develop a more
comprehensive sampling program for consideration by the
CEC.
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Sampling Objectives
o to obtain soil and crop tissues from a field located as close to the edge of the lagoon
as possible to represent a maximum potential for contamination in this initial area of
study;
o to sample as many different species of crops as possible;
o to collect samples of crop tissues that would represent both human and animal
consumption;
o to ensure that when crop tissues were sampled, a corresponding sample of soil from
the 0-15 cm plough layer (rooting depth) was sampled;
o to obtain soil and crop samples from the southeastern area of the lagoon where
water rises and falls depending on seasonal rainfall and eventually seeps into the
neighbouring fields;
o to obtain surficial soil (0-5 cm depth) from an area in La Zacatecana where children
would be exposed to the greatest extent;
o to obtain soil from an unpaved dirt road in the village of La Zacatecana which, during
dry times of the year, would be a source of wind-blown dust exposure; and,
o to obtain a surficial soil sample from an area remote from La Zacatecana to gain
insight on the natural background concentrations of chemical parameters selected for
analysis.
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Site Selection
Site Number
Site Description
Soil Depth Sampled
(cm)
Vegetation Type
1
Farm Field – West of La
Zacacetana
0-15 cm
Corn leaves
Bean seeds
2
School Playground – La
Zacacetana
0-5 cm
No vegetation
3
Unpaved Dirt Road – La
Zacacetana
0-5 cm
No vegetation
4
Farm Field – NW edge of
lagoon
0-15 cm
Corn leaves
Corn kernels
5
Farm Field – SE edge of
lagoon
0-15 cm
No vegetation
6
Farm Field – SE edge of
lagoon
0-15 cm
Green Bean pods
7
Mountain parkland – N of
Zacatecas
0-5 cm
No vegetation
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Site 1
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Site 2
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Site 3
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Site 4
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Site 5
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Site 6
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Site 7
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Sampling of Soil and Vegetation
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Summary of Findings
Ontario
Criterion Agr.
& Res/Park
Coarse/Fine
Texture
(ug/g)
Site 1
Site 2
Site 3
Site 4
Site 5
Site 6
Site 7
Farm Field
ug/g
School
ug/g
Road
ug/g
Farm Field
ug/g
Farm Field
ug/g
Farm Field
ug/g
Park Area
Hg
10
1.3
13
12
28
2.5
1.1
2.0
As
20/25
21
16
20
82
12
7.8
18
Cd
3/4
ND
1.5
0.97
8.8
0.34
ND
2.1
Pb
200
44
170
140
550
36
17
460
Zn
600/800
82
220
180
1000
48
25
440
E.C.
(uS/cm)
700
230
670
1300
1200
190
110
250
Chemical
ug/g
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Chemical Parameters Analyzed
Soil
 pH, Hg, Methyl Hg, As, Sb, Ba, Be, Cd, Cr, Cr VI, Co,
Cu, Pb, Mn, Mo, Se, Ag, Tl, V, Zn
 E.C., CN, Nitrite, Nitrate, Sulphate, SAR, B, Fe
 TCLP Inorganics
Vegetation
 Hg, Methyl Hg, Al, Sb, As, Ba, Be, Bi, B, Cd, Cr, Co,
Cu, Fe, Pb, Mn, Mo, Ni, Se, ag, Sr, Tl, Sn, Ti, U, V, Zn,
Sulphur
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Summary of Findings
Soil
 Soil exceeded ecological or human health risk-based criteria
at four of the seven sites;
 Chemical parameters found to exceed Ontario’s site
remediation criteria included:
• Arsenic
• Cadmium
• Lead
• Mercury
• Zinc
• Electrical Conductivity (EC)
 Contamination was greatest at Site 4 (Corn field -NW side of
lagoon);
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Summary of Findings (cont’d)
Soil
 Soil from farm fields SE of the lagoon did not exceed any
criteria;
 Soil from the school playground and unpaved road exceeded
only the mercury criterion which is based on vegetation
protection;
 Soil from the control site north of Zacatecas (Paseo de la
Bufa) exceeded the soil criterion for lead.
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Summary of Findings
Soil – Hazardous Waste Classification
 None of the TCLP leachate analyses (including Hg,
As, Pb and Ag) exceeded Ontario’s drinking waterbased criteria
 Based on these findings, the soil from the sampled
sites would be classified as non-hazardous
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Summary of Findings
Vegetation
 Concentrations of mercury and other related contaminants in
vegetation from the field where soil quality criteria were exceeded
were elevated and warrant further investigation in terms of the risk
posed from consumption;
 Methyl mercury, the most toxic form of mercury in terms of human
health, was found in very low concentrations in all vegetation
samples, with the highest concentrations being 4 orders of
magnitude (30,000-40,000 times) lower than levels that were
recorded in contaminated flour that resulted in severe health
problems for people exposed to methyl mercury in Iraq
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Preliminary Conclusions
 mercury and other related contaminants are present in soils of some farm fields
in the La Zacatecana area at concentrations in excess of risk-based human and
ecological criteria;
 Concentrations of mercury and other related contaminants were not detected in
concentrations exceeding criteria which are used in Ontario for the remediation
of sites to levels considered acceptable for residential/parkland use;
 Concentrations of methyl mercury in vegetation were very low in comparison to
dietary exposure levels reported in a study of health impacts in another country;
 Concentrations of mercury and other related contaminants in vegetation from the
field where soil quality criteria were exceeded were elevated and warrant further
investigation in terms of the risk posed from consumption
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Preliminary Conclusions
 Based on the foregoing findings, a more
comprehensive assessment of the degree and extent
of mercury and related chemical contamination
throughout the entire zone where mine tailings are
known to have accumulated over the past 500 years
appears warranted to provide input data for
assessment of potential human and ecological health
impacts.
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The CEC and Mexican Team
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