A simple and fast screening test to detect soils polluted by lead

Environmental Pollution 118 (2002) 285–296 www.elsevier.com/locate/envpol

A simple and fast screening test to detect soils polluted by lead Guy Merciera,*, Jose´e Duchesneb, Andre´ Carles-Giberguesc a INRS-Eau, 2800 Einstein Street, Sainte-Foy, Que´bec, Canada G1V 4C7 De´partement de ge´nie ge´ologique et ge´ologie Universite´ Laval, Que´bec, Canada, G1K 7P4 c INSA, Department of Civil Engineering, Complexe scientifique de Rangueil, 31077 Toulouse cedex 4, France b

Received 28 May 2001; accepted 16 October 2001

‘‘Capsule’’: GJST solubilized more lead than did the toxicity characteristic leaching procedure (TLCP). Abstract Lead pollution is an environmental priority. The evaluation of contaminated soils was often based on the results of the toxicity characteristic leaching procedure (TCLP) or the synthetic precipitation leaching procedure (SPLP). This paper presents a simple and fast screening test to detect soil contaminated by lead. The test is based on the chemistry of the stomach (Cl concentration, pH 2, T=37  C) and simulates the incidental oral ingestion of soil by young children. The gastric juice simulation test (GJST) and the TCLP were applied to six size fractions from five soils. The GJST solubilized more Pb (up to 169 mg/l) than the TCLP especially for the smallest size fraction. Particle size had less effect on the TCLP. The percentage of lead released with the GJST, was most significant for the < 63 mm size fraction and varied from 18 to 74% of the total lead content. Lead leached during the TCLP as a function of the total lead content showed poor linear regression coefficient (R) values for soils < 250 mm. R values were significant for all size fractions with the GJST. The pH of approximately 5 in the TCLP limits the solubilization of lead in the small size fractions. The five soils exceeded the toxicity threshold of 10 mgPb/dl of blood for a significant fraction of children between 0 and 36 months using the EPA’s IEUBK model (Integrated Exposure Uptake Biokinetic). But the TCLP did not detect lead contamination in two of these five soils. The GJST proved to be a better estimator of lead bioaccessibility in the gastrointestinal tract. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Lead; Polluted soils; Gastric juice; Detection; Chemical availability; IEUBK; Gastro-intestinal tract; Toxicity; Children

1. Introduction 1.1. Lead, an environmental priority The goal of this work is to develop a simple and fast screening test to detect lead-contaminated soils as lead is a priority on the list of toxic elements in the United States (Xintaras, 1992) and in many countries. This paper does not pretend to present a toxicological test. When a soil is identified as problematic using the proposed test, a more detailed risk assessment must be done. Children under the age of 5 are most at risk (Xintaras, 1992; USEPA, 1994). Direct oral ingestion of contaminated soils and dust by children is the principal cause of lead absorption (Healy et al., 1982; Xintaras, * Corresponding author. Tel.: +1-418-654-2633; fax: +1-418-6542600. E-mail address: [email protected] (G. Mercier).

1992; USEPA, 1994). Lead present in soils and dust at concentrations of 500–1000 mg/kg can affect children’s health (Xintaras, 1992). In the United States, a detailed analysis of 12 epidemiological studies (Lanphear et al., 1998) showed that 5.9% of American children had more than 10 mg Pb/dl in their blood. This value is the threshold above which neurotoxicity from lead occurs (USEPA, 1994; Lanphear et al., 1998). Many of the studies concerning lead availability from soil have been carried out on soils polluted by mining activities or by lead smelters (Davis et al., 1992, 1993, 1997; Ruby et al., 1992, 1993, 1994, 1996; Gasser et al., 1996). However, there are other sources of lead pollution such as the spreading of sewage sludge, gas emissions from cars (Wixon and Davies, 1993). Several lead battery recycling sites have also been contaminated by lead (Nedwed and Clifford, 1997). Some sites are contaminated by the spreading of ash from incinerators and by the presence of metals workshops in the past (Option

0269-7491/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(01)00307-4

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Ame´nagment, 1992). Lead pigment in paints has also been an important source of contamination. Those pigment were lead carbonate, sulphate as well as basic lead carbonate (2PbCO3.Pb(OH)2) and other lead compound (3PbO.2SiO2.H2O and 4PbCO3.2Pb(OH)2.PbO). Red lead (Pb3O4) was used abundantly in the past, as was PbCrO4 or PbCrO4.PbO for yellow colouring. Chipping paint is a significant source of contamination in soils near buildings (Xintaras, 1992) and is a problem in old housing (USEPA, 1994). 1.2. Size of particles and quantity ingested An important parameter used to evaluate environmental risk is the particle size fraction (SF) that is considered to be bioavailable. This evaluation must be realistic. Some studies consider only the fraction smaller than 250 mm to be involved in oral contamination in children (Davis et al., 1992, 1993, 1997; Ruby et al., 1992, 1993, 1994, 1996; Gasser et al., 1996; Zhang and Ryan, 1998). These studies are based on the work of Duggan et al.’s (1985) which concludes that only soil particles of a diameter smaller than 250 mm should be considered. However, Duggan et al. (1985) did not study pica (intentional absorption of relatively large quantity of soil) or incidental absorption from the playground (small amount of soil ingested daily in the playground) in children aged 0–4 years. Their goal was to evaluate the absorption of lead in children (5 and 6 years of age) from the particles that stick to their hands (< 100 mm). The United States Environmental Protection Agency (EPA) states that young children eat paint chips of several millimeters in size (USEPA, 1994). If children can consume paint chips measuring several millimeters in diameter, then they can certainly consume sand and soil particles of similar dimension. Indeed, most parents report that young children sometimes eat soil and sand particles measuring up to 1 or 2 mm in diameter. It seems unrealistic to consider only particles smaller than 250 mm, especially without taking into account the quantity ingested. The EPA considers that, on average, a child takes in 135 mg of soil and dust per day. The Superfund program (US government program to decontaminate soils) uses a value of 200 mg per day for site evaluation. In some cases, however, children can consume up to 10 g/day (Kimbrough et al., 1984; Calabrese et al., 1989). 1.3. The dynamics of the gastrointestinal (GI) tract The stomach is a complex system and is much more active following a meal. The pH of an empty stomach is between 1.5 and 2.5. When the ingestion of a meal begins, the pH increases to a value between 4 (Sleisenger et al., 1993) and 7 (Gue´nard 1991). Then the production of HCl and enzymes starts quickly and the pH is

gradually reduced to a value between 1.5 and 2 after 3 h (Gue´nard, 1991). The concentration of HCl can reach 0.150 M. During this time, the contents of the stomach are mixed by peristaltic movement. Little absorption occurs in the stomach. In children, the stomach retention time varies from 2 h (Ruby et al., 1992) to less than 4 h (Vick, 1984). After spending this time in the stomach, the pyloric sphincter let passes a higher flow of food (ml per min) into the duodenum (Guyton and Hall, 1996) where it remains for approximately 1 h (Ruby et al., 1996). Absorption begins as the food enters the duodenum, and pH increases gradually due to the production of bicarbonates and other agents by the pancreas (Gue´nard, 1991; Ruby et al., 1992). Thereafter, absorption continues at a neutral or basic pH as the food advances to other parts of the small intestine. Lead solubility increases considerably in the presence of chloride due to the formation of chlorocomplexes in acid media (Ruby et al., 1993, 1999; Gasser et al., 1996; Mercier et al., 1996). 1.4. Bioavailability The oral bioavailability is defined as the fraction of an administrated dose that reaches the blood, it is commonly referred to as ‘‘absolute bioavailability’’. The oral bioaccessibility is the fraction that is soluble in the gastrointestinal environment and is available for absorption. The lead that does not enter the bloodstream is excreted. The Integrated Exposure Uptake Biokinetic (IEUBK) model for lead in children used by the EPA is based on this definition (USEPA, 1994). Bioavailability varies according to the solubility of the product, the size of the particles, the composition of the gastric juice, the temperature and the extent of mixing in the stomach. Lead carbonate is one of the most highly bioavailable lead compounds (Barltrop and Meek, 1975). The solubility product (Ksp) is used to calculate the concentration of the ions at equilibrium, but without taking into account the time required to reach this state. Gasser et al. (1996) showed that equilibrium is often not reached in the GI tract. In fact, bioavailability depends more on the kinetics of the solubilization of the solid phase than on Ksp. It is directly related to the retention time in a given medium (Gasser et al., 1996). The bioavailability of lead in children varies from 30 to 40% and depends on the nutritional status of the children (Goyer, 1991; Wixon and Davies, 1993; Gasser et al., 1996; Ruby et al., 1996). The EPA considers values from 5 to 40% and uses a default (or standard) value of 30% in IEUBK model (USEPA, 1994). Ruby et al. (1993) measured bioavailability levels as low as 9% in the stomach of a rabbit (in vivo) for soil contaminated by mining activities. This soil contained lead-bearing phases of low bioavailability, including galena (PbS) covered with anglesite (PbSO4),

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anglesite coated with jarosite (NaFe3(SO4)2(OH)6), and galena included in quartz (SiO2) or pyrite (FeS2) (Ruby et al., 1992), arrangements constituting a physical barrier to solubilization. 1.5. A simple screening test Up to now, the most widely used test to evaluate polluted sites in the USA is the toxicity characteristic leaching procedure (TCLP; USEPA, 1994). The synthetic precipitation leaching procedure (SPLP) is also used (USEPA, 2001). SPLP has a pH of 4.2, uses sulfuric and nitric acid and has a completely different composition than the gastric juice. Total content is also used as criterion. Many researchers concluded that the soil they treat is decontaminated and can stay on site using the TCLP (Legiec, 1997; Marino et al., 1997; Van Benschoten et al., 1997; Willilford et al., 1999; Cooper et al., 1999; Sheets and Bergquist, 1999). According to the USEPA and considering the past experiences, the TCLP can be used in many ways. Here is a citation of an email obtained from the Mice service of the USEPA concerning the use of the TCLP for soil characterisation: ‘‘Later in the process, as EPA decides on possible remedies, they may use the TCLP to determine how much material may leach into the groundwater under the site and therefore pose a risk to persons off-site through groundwater contamination’’ (Mice, 1999). From the minutes of a meeting (USEPA, 1999a), one can see that most experts recommend the use of other tests to estimate metal availability from soil. However, the previous sentences prove that the TCLP is often employed to judge if a soil presents a threat to the environment and humans, if treatment is required. A new simple and economical test is needed. If the results of the TCLP exceed the threshold value of 5 mg Pb/l, the soil is considered to be contaminated, and further investigation is carried out, sometimes using the IEUBK model. During the TCLP, which uses acetic acid, the actual pH often ranges between 4.8 and 5.2, with the extraction liquid at a pH of 4.93. This pH differs considerably from the pH of the stomach at the onset of nutrient (and lead) absorption. The purpose of the TCLP is to simulate the production of acetic acid in a landfill. In the stomach, however, the pH drops to approximately 2, due particularly to the presence of hydrochloric acid (Vick, 1984; Gue´nard, 1991; Scully and White, 1991), and the Cl concentration is at least 0.01M. Acetic, citric, malic and lactic acids are also present in the stomach, as is pepsin, a major enzyme (Ruby et al., 1993). An in vitro test simulating gastric juice was developed by Ruby et al. (1993), but improvements to this test are in progress (Ruby et al., 1999). This test confirms that the ions H+ and Cl control the dissolution of the lead mineral in the stomach. It also shows that enzymes and organic acids are

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necessary to maintain lead in a soluble form when it enters the small intestine. However, Ruby’s test is too complex to be used as a screening test and they search to develop a more simple and economical screening test. Zhang and Ryan (1998) developed a test using a Cl concentration of 0.001M, but this concentration is not representative of the real concentration in the stomach. The aim of this paper is develop a simple and fast screening test which simulates incidental adsorption of lead to detect problematic soils. Results will be compared to the TCLP data for several soil size fractions (SF). Using HCl and an organic acid, this new test simulates the stomach environment at the time when the food is pushed into the duodenum. However, the test must remain simple and economical if it is to be used widely in laboratories in order to detect lead problems. When this test detects a problem, more toxicological study needs to be done on the site.

2. Material and methods 2.1. Origin and first characterization of the soils Soils from three different urban sites were sampled. Three samples were taken at site 1 (1A, 1B, 1C). These soils were selected to represent various concentrations of lead, soils 1A, 1B and 1C having low, medium and high concentration of lead, respectively. Each of these composite samples comes from a different part of approximately 1 m3 of soil and represents the mean concentration of a compound in this volume. During sampling, any pieces bigger than 10 cm were removed. These were composed mainly of waste materials, bricks, stones, concrete slab, asphalt, leather, glass, and melted parts (garbage incinerator residues). The samples, weighing from 6 to 14 kg, were sieved on-site over a screen with 1-cm2 openings. The soils in this study had a particle size of less than 2 mm. The pH of the soil was measured in a mixture of one part of demineralized water and one part soil < 1 cm. The first soil (1A, 1B, 1C) was polluted from landfilling lowlands with waste and bottom ash from a municipal waste incinerator (1940–1955). The site was also used to store de-icing salt and snow and received unknown quantities of industrial waste. The soil at site 2 was also contaminated by municipal waste incinerator ash (1940–1955), as well as by different metals working industries (Option Ame´nagement, 1992). The sample from this site was a composite sample taken over a surface measuring 66 m and a depth between 0 and 2 m, at the time of loading a truck. Site 3 was contaminated primarily by the spreading of ash from coal burned for heating in the first half of this century. The sample from this site was a composite sample taken in the first meter of depth. All five soils are urban soils.

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The samples were dried at 80  C and sieved to 2 mm on a Sweco sieve measuring 45 cm in diameter. All the samples were obtained using a splitter. The < 2 mm fraction of each soil was sieved into 6 size fractions using a Rotap apparatus. The size fractions were in mm: < 63, 63–125, 125–250, 250–500, 500–1000, and 1000– 2000. The subsamples were crushed to < 50 mm using a Spex type crusher before undergoing chemical analysis. The percentage of sand was determined by sieving, sand being defined as the fraction > 63 mm and < 2 mm. The < 63 mm fraction was tested on a laser granulometer. The clay fraction was the fraction < 2 mm while the silt fraction was the 2–63 mm fraction.

possible to detect the presence of lead and to identify most of the elements associated with lead in this zone of the particles. The particle type was also noted (lead included inside or on the surface (at the edge) of the particle, with or without iron oxide). The dimensions of the lead-bearing particles were noted and their surfaces were measured by manual operation of the image analyser (software Noran TN8602-5). The main carrying particles were also identified using the EDS. Readers must note that most of the lead bearing particles are composed of two or more compounds. The lead bearing compound is called the lead-bearing phase (LBP) while the other zone of the particles is the carrying phase (CP), which can be anything like silicate, iron oxide, calcite, elemental copper, etc. . ..

2.3. Chemical analysis

2.5. TCLP and the gastric juice simulation test (GJST)

The crushed subsamples underwent a total digestion with HNO3-HF-H2O2 according to the standard method of the American Public Health Association (APHA, 1995). Certified samples were analysed as a control. Lead, cadmium, zinc and copper contents were determined using an atomic absorption spectrophotometer (Varian SpectrAA 20). Total carbon, organic and inorganic carbon, total nitrogen and total sulphur were analysed (Environnement Canada, 1992) with a Carlos Erba thermal analyser.

Pepsin is a major enzyme of the stomach and the addition of this compound in the GJST is questionable. Firstly although medical laboratories often work with enzymes, most chemical analysis laboratories do not routinely use an enzyme like pepsin. So it will add to the complexity of the test and prevents its widespread use. Secondly will pepsin always behave in the same manner in the test? The use of pepsin in the test could ameliorate the GJST but it would increase its complexity and the variability of the results. So the authors decided to omit pepsin addition. The TCLP is run on a filtered solid of a diameter of less than 9.5 mm (30) rather than on a dried solid (Federal Register, 1990). In this study, the results of the TCLP and the GJST were compared for various size fractions (SF) to determine chemical availability. The proportion of dry solid was maintained constant. Fortyfive grams of dry soil were used per liter of extraction fluid. All tests were run in duplicate. In the GJST, 6 ml of glacial acetic acid (99.7%) were added to 8 l of demineralized water heated to 37  C in a water bath. Acetic acid was selected because it is present in the stomach (Ruby et al., 1993). To keep the screening test as simple as possible, no other organic acid or enzyme was added. Fig. 1 presents the experimental protocol of the GJST. The 45 g of dry solid were placed in the bottle with the extraction liquid, in a liquid/solid (L/S) ratio of 22.2. Ruby et al. (1993) used an L/S ratio of 10 to represent the stomach of a rabbit. Higher L/S ratios have been used by other researchers (Gasser et al., 1996; Zhang and Ryan, 1998). An L/S ratio of 22.2 represents a ‘‘worst case’’. Concentrated HCl 12 M was added over a 20-min period to obtain a pH of approximately 6. The samples were agitated for 20 min on an agitator appropriate for the TCLP. The samples were returned to the water bath and were acidified with HCl to a pH of 4 over another 20-min period. These operations were repeated for a pH value of 2.5 and 2, as

2.2. Sample preparation

2.4. Mineralogy and microanalysis technique Polished thin sections measuring 2545 mm were prepared from the subsamples using diamond powder as a polishing agent. The energy dispersive spectrophotometer (EDS) of the Scanning Electron Microscope (SEM) (Jeol 840A) cannot resolve the K lines of sulphur (2.31 kV) and the M line of lead (2.34 kV). The wavelength dispersive spectrophotometer (WDS) of the electron probe micro analyser (EPMA; Cameca SX100) was therefore used to detect the presence of lead sulphides or sulphates. A one-micron beam and a current of 15 kV and 20 nA were used. Various pure minerals were used as standards for the calibration of the EPMA and the ZAF correction program was used for the calculations. The particles containing lead-bearing compounds were detected with the backscattered electron image (BEI) operating mode. The EPMA provides a quantitative analysis (Fe, Zn, Cu, Ti, Ca, Pb, S, Sn, Sb, Ba, P, Al, Si, O) of a sample volume of approximately 5 mm3. The particles were selected randomly over the surface of the polished thin section. The SEM was used to identify a large number of particles containing lead-bearing compounds. Seven hours of operation were allowed for each sample. The whole surface was slowly scanned with the BEI mode to locate the particles with lead-bearing compounds. An X-ray analysis with the EDS made it

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indicated in Fig. 1. At the end of the extraction, the samples were left to settle for 5 min and 140 ml of the supernatant liquid were filtered through Whatman GFF paper. The samples were acidified to a pH of less than 1 with 7 ml of concentrated HNO3. The total duration of the test was 160 min  10 min. The temperature was maintained between 35 and 39  C. Eight tests were run simultaneously. The test simulates the dynamics of the stomach by duplicating the gradual fall of the pH, the temperature and the intermittent mixing. The GJST integrates the kinetic aspect associated with oral ingestion. The tests were repeated when the difference between the duplicates was higher than 1 mg/l for a result between 0.0 and 5.0 mg/l (TCLP or GJST), or when the relative variation exceeded 20% for results higher than 5 mg/l. Less than 10% of the tests were repeated.

3. Results and discussion 3.1. Physicochemical characterization of the soils Table 1 shows the chemical and physical characteristics of the < 2 mm SF. Soils from sites 1A, 1B and 1C were slightly basic soils with pH values of 7.1, 7.7 and 7.6, respectively. Total carbon was relatively abundant and was mainly in the form of organic carbon. Soil 2 was highly basic with a pH of 9.2 and soil 3 was fairly basic with a pH of 8.2. In all cases, the nitrogen and

total sulphur contents were relatively low. The presence of anglesite and galena was judged unlikely. Data on clay, silt and sand indicated that all soils were passably sandy as soils contained between 77.2 and 91.9% of sand (Table 1). Table 2 presents the lead contents of the samples. Six soil fractions were analysed as was the total < 2 mm sample from each soil. The theoretical error of analysis was 4%, and the error of analysis for the six analyses thus totalled 24%. The maximum error was 18%, falling within the theoretical error margin. Various levels of lead contamination were detected. Sample 1A showed relatively low lead contamination with 924 mg Pb/kg, whereas sample 1C presented a high level of contamination with 7518 mg Pb/kg. Sample 1B was contaminated by lead at a medium level (4013 mg Pb/kg). 3.2. Mineralogical analyses of the soils The results of the EPMA are presented in Table 3. Lead carbonates can often be differentiated from lead oxides. Cerussite (PbCO3) and basic lead carbonate (2PbCO3.Pb(OH)2) contain 77.5 and 75.4% Pb, 18 and 15.5% O, and 4.5 and 8.7% C, respectively, whereas lead oxides contain 86.6, 90.7 and 92.8% Pb, and 13.4, 9.3 and 7.2% O for PbO2, Pb3O4 and PbO, respectively. The oxides do not contain carbon, which implies that the sum of the element analyses must equal 100% if a pure lead-bearing phase is analysed. In the case of carbonates the sum of the elements ranges between 92 and 96% since carbon is not analysed. Table 3 clearly shows that in all samples except soil 3, lead carbonate was the

Fig. 1. Schematic representation of the protocol of the gastric juice simulation test (GJST).

Table 1 Chemical and physical characteristics of the <2 mm soil size fraction Site

pH

Total carbon (%)

Organic carbon (%)

Inorganic carbon (%)

Total nitrogen (%)

Total sulfur (%)

Clay (%)

Silt (%)

Sand (%)

1A 1B 1C 2 3

7.1 7.7 7.6 9.2 8.2

7.26 8.76 10.17 1.96 17.57

5.78 7.42 8.39 1.18 12.46

1.47 1.35 1.78 0.79 5.11

0.14 0.22 0.29 0.14 0.36

<0.3 <0.3 <0.3 <0.3 <0.3

1 1.5 1.6 0.8 2.7

7.1 13.9 21.2 9.8 11

91.9 84.6 77.2 89.4 86.3

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Table 2 Lead content and mass balance for the various size fractions Site

Size fraction (mm)

1A

1000–2000 500–1000 250–500 125–250 63–125 <63 Sum of the fractions <2 mm sample analysis Difference

0.113 0.304 0.262 0.159 0.082 0.081 1.000

1126 836 762 684 831 1405

127 254 199 108 68 114 871 924 5.7%

1B

1000–2000 500–1000 250–500 125–250 63–125 <63 Sum of the fractions <2 mm sample analysis Difference

0.160 0.232 0.235 0.137 0.082 0.154 1.000

2661 2800 2657 3708 4812 5982

425 649 625 508 397 919 3523 4013 12.2%

1C

1000–2000 500–1000 250–500 125–250 63–125 <63 Sum of the fractions <2 mm sample analysis Difference

0.174 0.187 0.183 0.125 0.103 0.228 1.000

8784 6621 5989 6244 7108 6442

1533 1236 1098 782 729 1467 6845 7518 9.0%

2

1000–2000 500–1000 250–500 125–250 63–125 <63 Sum of the fractions <2 mm sample analysis Difference

None 0.064 0.200 0.381 0.248 0.106 1.000

1486 1280 1721 4077 5078

95 256 656 1013 540 2560 2204 16.2%

1000–2000 500–1000 250–500 125–250 63–125 <63 Sum of the fractions <2 mm sample analysis Difference

0.185 0.213 0.223 0.143 0.103 0.134 1.000

1338 2099 1951 2114 2480 2965

248 446 434 301 255 397 2082 2457 18.0%

3

Proportion of the size fraction

most abundant form. Cerussite and basic lead carbonate cannot be differentiated. Often the analysis for denomination carbonates and lead oxides is used because it is not always possible to differentiate between them. Sample 3 contained mainly lead carbonate and lead oxide, but the lead was more often associated with barite (BaSO4). The silicates, the phosphates and the mixed oxides of lead and iron and/or Mn were rarer. Neither galena nor anglesite was found with the EPMA

Pb analysis (mg/kg)

Pb content by size fraction (mg/kg)

in the soils studied, and the total sulphur content in all samples did not exceed 0.3% (Table 1). Table 4 presents the results of the analyses performed with the SEM. Lead carbonate was the most abundant form in the five samples. In samples 1A, 1B, and 1C, the other lead-bearing particles were silicates, oxides and phosphates. Mixed carbonate-oxides of lead and tin (PbaSnb(CO3)cOd) were also present. The carrying phase was generally silicate. In sample 1B, the lead-bearing phase was often linked

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G. Mercier et al. / Environmental Pollution 118 (2002) 285–296 Table 3 Results of the analyses done with the electron probe micro analyser Site

Pb-carbonate

Pb-oxide

Pb-carbonate+oxide

Pb-silicate

Pb-phosphate

PbFeMn-oxide

Pb-carbonate+oxide and Pb in barite

1A 1B 1C 2 3

5/7 28/47 6/11 8/13 3/10

1/7 2/47 3/11 0/13 0/10

1/7 9/47 1/11 3/13 3/10

0/7 3/47 0/11 1/13 0/10

0/7 3/47 1/11 1/13 0/10

0/7 1/47 0/11 0/13 1/10

0/7 1/47 0/11 0/13 3/10

to elemental copper. In soils 2 and 3, Pb was also present as carbonate and as mixed lead-titanium carbonate (PbaTib(CO3)cOd). Soil 3 also contained a combined lead-chromium oxide (probably chromate, in paint). The carrying phase in soil 2 was mostly silicate followed by iron oxide or titanium oxide. For soil 3, both the slag (Pb,Cu, Zn,S,Fe)CaSiO4 (Davis et al., 1993) and the organic matter or coal residue (C in Table 4) were contaminated. The carrying phase in soil 3 was also iron oxide or titanium oxide. For soil 3, silicate was less important. The percentage of the surface containing lead-bearing phases was high for the small particles (66.4 to 96.5% for < 63 mm) and low for the large particles (4 to 35.5% for > 1000 mm). For a same soil, the percentage of particles where the lead-bearing phase was included inside the particle was low for the small particles. However, it was significantly higher (33.3–66.6%) in particles > 1000 mm. Chemical availability in the large particles was therefore theoretically lower. 3.3. The TCLP and the GJST Table 5 presents the results of the TCLP and the GJST. The GJST leached more Pb than the TCLP. With the GJST, the amount of lead released decreased quickly as the size of particles increased. Table 6 presents the linear regressions between the effective solubilization of lead during the test and the total lead contents for the five different soils. Data were grouped according to size fraction. The coefficient of linear regression (R) is excellent for the GJST especially for the 500–1000, 1000–2000, < 63, and 63–125 mm size fractions. The strong R values indicate that the mineralogy of the various soils is quite similar and does not result in different levels of solubilization. The fact that lead carbonate and oxide are the main lead-bearing phases for all the soils and that they are relatively soluble salts of Pb explain this homogeneity in solubility results. If there were some soils with much galena (PbS) (Kps of 10 27.5) or other highly insoluble lead compounds (pyromorphite (Pb5(PO4)3Cl; Kps 10 84.4), plumbogummite (PbAl3(PO4)2(OH)5H2O; Kps 10 99.3), corkite (PbFe3PO4SO4(OH)6; Kps 10 112.2), hinsdalite (PbAl3 PO4SO4(OH)6; Kps 10 99.1; Davis et al., 1993), in

the data used for the statistical analysis then it would reduce very significantly the regression coefficient value relating soluble lead during GJST to total lead content. These highly insoluble lead compounds would be much less soluble in the GJST for the same total lead content. The results from the mineralogical study are important to explain the solubility of Pb in the GJST. For the 125– 250 and 250–500 mm size fractions, the R values for the GJST (0.653 and 0.605, respectively) are lower but still significant. For the TCLP, the R values are high for the three coarsest fractions and very low for the three finest fractions. The pH of approximately 5 used in this procedure is not acidic enough to solubilize more lead in the smaller size fraction. Therefore, the TCLP cannot accurately predict lead solubility in the GI tract. When SF is included as a variable, R values increase from 0.679 to 0.745 for the GJST and from 0.533 to 0.671 for the TCLP. These results indicate that SF must be taken into consideration even if its effect is less significant than the total lead content of the soil. The GJST better simulates the chemistry of the GI tract system. Because the TCLP uses no chloride, a relatively high pH (  5) and a low temperature (20  C), it does not adequately represent solubilization in the GI tract. Some researchers believe that metals are not absorbed at a pH of 2, because the pH goes up to 7 in the small intestine. However, there is a kinetic effect to consider. Absorption actually begins as the food passes from the stomach to the duodenum. At this time the pH is as low as 2, and sometimes 1.5. Neutralization to a pH of 7 takes about one hour. Logically then, the pH can be expected to increase from 1.5–2 to 4.5 over one period of about 30 min. In fact, when the pH in the entrance of the duodenum is lower than 3.5–4.0, the reflexes block further release of acidic stomach content to avoid ulcer (Guyton and Hall, 1996). MINEQL+ (Chemical equilibrium calculation program), with total Pb=8.5410 4 M, Cl =510 2 M, SO4 2=1.510 3 M, CO3 2=110 3 M and pCO2=10 3.5 atm at a pH of 2, shows soluble lead to be equal to 100% or 177 mg Pb/l at equilibrium, mainly in the form of chlorocomplexes. At pH 4.5, 16.66 mg/l mg Pb/l is still soluble at equilibrium., equilibrium is probably not reached in 30 min. During the gradual increase of pH from 2 to 4.5, lead is not completely precipitated and the body

292

Table 4 Mineralogy according to the results with the scanning electron microscope on polished thin sectionsa Units (mm)

1A

< 63 63–125 125–250 250–500 500–1000 1000–2000

100 57 50

< 63 63–125 125–250 250–500 500–1000 1000–2000

40 56 80 36 92 89

< 63 63–125 125–250 250–500 500–1000 1000–2000

65 53 55 56 55 33

< 63 63–125 125–250 250–500 500–1000 1000–2000

85 73 50 50 22

< 63 63–125 125–250 250–500 500–1000 1000–2000

46 22

1B

1C

2

3

a

Pb-carb. (%)

75 33

Pb-carb. +oxi. (%)

Pb-oxi.

33 33

80 88 50

PbFe-oxi (%)

11 11 9 33

13 17 7 36

15 16 9 17

PbSn-carb.+ oxi. (%)

17

25 17

Pb-sil. (%)

14

Carrying phase (CP)

Mean surface of CP (mm2)

Pb incl. volume (%)

75 65 5 35 17 36

None > sil. Sil. Fe-oxi. > sil. Sil. Sil. Sil.

640 6250 40,000 82,500 32,4000 1,560,000

25 17 33 33 57 50

75 83 67 67 43 50

7

86 51 42 36 31 17

Sil. > cal. Sil. > cal. Sil. > bar. Sil. > Cu0 Sil.+bar.+Cu0 Cu0+Ti-oxi.

1373 3947 14,718 63,750 300,000 866,000

0 22 40 36 8 33

100 78 60 64 92 67

8 5 18

78 60 59 37 31 35

Sil. > bar. Calc. > bar. Sil. > bar. Sil. > cal. Sil. Sil.

1160 4686 16,500 44,700 186,000 900,000

25 26 18 28 91 67

75 74 82 72 9 33

97 83 60 32 4

None > sil. None > sil. Sil. > Ti-oxi. Sil. > Fe-oxi. Sil.=Fe-oxi.

950 3700 14,000 83,700 610,000

0 5 0 40 67

100 96 100 60 33

75 51 30 17 4 22

None > sil. Fe-oxi.+C Slag > sil. Fe-oxi. > sil. > C Slag > Ti-oxi. > C Sil. > Slag=Ti-oxi.=C

1100 3400 28,300 54,500 254,000 2,125,000

0 11 0 40 50 40

100 89 100 60 50 60

Pb-sulf. (%)

Pb-CrO (%)

PbTi carb.+ oxi. (%)

13

14 50 13

6 7

4 5 9 9

8 5

9

17 13 21 8 11

5 9 11 18

6

33 3

5 10 13

13 22

5 14 10 25 22 None 15

22

11 33

33

8 9 20 22

8 11 33 20

Pb surface (%)

Mean % Pb-bearing phase (%)

Pb-phos. (%)

67 14

13 6

Pb-met. (%)

10 11

23 22

13 25

8 11

25

carb., Carbonate; met., metal; phos., phosphate; CrO, probably chromate; bar., barite; oxi., oxide; sil., silicate; sulf., sulphate; cal., calcite.

G. Mercier et al. / Environmental Pollution 118 (2002) 285–296

Site

G. Mercier et al. / Environmental Pollution 118 (2002) 285–296 Table 5 Lead leached by the toxicity characteristic leaching procedure (TCLP) and the gastric juice simulation test (GJST) Site Size fraction (mm) Pb leached by GJST

Pb leached by TCLP

(mg/l)

(%)

(mg/l)

(%)

1A

<2000 1000–2000 500–1000 250–500 125–250 63–125 <63

8.1 4.7 6.1 6.5 5.5 9.9 32.2

19.4 9.3 16.2 18.9 17.9 26.5 50.9

2.6 0.7 0.2 1.5 1.2 0.9 0.2

6.3 1.4 0.5 4.4 3.9 2.4 0.3

1B

<2000 1000–2000 500–1000 250–500 125–250 63–125 <63

31.6 34.2 35.5 26.3 27.1 71.2 149.5

17.5 28.6 28.2 22.0 16.2 32.9 55.5

10.1 18.0 1.6 7.2 5.0 5.2 4.7

5.6 15.0 1.3 6.0 3.0 2.4 1.7

1C

< 2000 1000–2000 500–1000 250–500 125–250 63–125 <63

68.6 67.3 38.4 32.2 36.3 147.0 163.6

20.3 17.0 12.9 11.9 12.9 46.0 56.4

12.0 50.2 27.1 12.5 4.7 4.2 4.4

3.5 12.7 9.1 4.6 1.7 1.3 1.5

2

<1000 1000–2000 500–1000 250–500 125–250 63–125 <63

57.6 None 24.2 29.5 38.5 89.1 169.1

58.1 None 36.2 51.2 49.7 48.6 74.0

31.8 None 5.2 5.0 25.9 28.3 25.4

32.1 None 7.7 8.7 33.4 15.4 11.1

3

< 2000 1000–2000 500–1000 250–500 125–250 63–125 <63

22.9 14.7 22.9 18.9 21.3 32.5 37.2

20.7 24.4 24.2 21.5 22.4 29.1 27.9

0.3 13.3 0.4 0.4 0.4 3.0 2.7

0.3 22.1 0.4 0.5 0.4 2.7 2.0

absorbs an unspecified part of this lead. The IEUBK model was used with all the default values except the soil lead content. The results show that for children aged 0–36 months and a soil with 906 mg Pb/kg, 27% of children would have more than 10 mg Pb/dl of blood if bioavailability was at 30%. If bioavailability was at 50%, the safety threshold would drop to 541 mg Pb/kg of soil. One must not forget the fact that IEUBK do not simulate pica eating but the oral ingestion of 135 mg of soil per day thus for child showing pica eating behaviours, the statistics would be worse. The maximum content permitted in residential soils in the province of Quebec is 500 mg Pb/kg (MEFQ, 1998). A risk analysis demonstrating the safe use of soils exceeding these values may allow the residential use of more highly

293

contaminated soils (MEFQ, 1998). In the USA, total metal content limits are based on risk assessments. Based on the TCLP, soil 1A (Table 5) is considered uncontaminated since the fraction < 2 mm released only 2.6 mg Pb/l, and the threshold above which more intense investigations must be carried out on a soil is 5 mg Pb/l (USEPA, 1994). With the GJST, the < 2 mm fraction of soil 1A released 8.1 mg Pb/l, a level regarded as problematic for residential use, but not necessarily for industrial or commercial use. However, this same soil released up to 32.2 mg Pb/l from the < 63 mm SF with the GJST. With the TCLP, on the other hand, only 0.2 mg Pb/l were leached for this same SF, a concentration 161 times lower. Table 5 shows that 50.9% Pb was leached from the < 63 mm SF with the GJST. The TCLP released only a small quantity of lead from all SF. Soil 1A contained 924 mg Pb/kg for the < 2 mm SF and exceeded the thresholds of toxicity calculated with IEUBK software for 30 and 50% bioavailability (906 and 541 mg Pb/kg, respectively). Often the TCLP was used to judge if a soil can stay on site after the treatment was done. These results raise serious questions about the use of the TCLP on a slightly contaminated soil like soil 1A, as this level of lead can be found in treated soils. However, it is important to remember that the GJST is an indicator of bioaccessibility in the gastric juice at the time of the passage of food in the duodenum where absorption begins, and it does not represent bioavailability as defined in the IEUBK model. Actual solubility in the GI tract vary from one meal to another according to nutritional status, pH and the concentration of Cl and of various other organic acids and enzymes. The presence of metal adsorbing or precipitating compounds or other factors will also influence bioavailability. Although soils 1B and 1C are located within 10 m of soil 1A, they are much more contaminated (Table 2). Results for the < 2 mm SF show that 31.6 and 68.6 mg Pb/l were released with the GJST and 0.1 and 12.0 mg Pb/l with the TCLP for sites 1B and 1C, respectively (Table 5). Based on the TCLP, these two slightly contaminated soils exceeded the threshold of 5 mg Pb/l. The GJST leached 149 and 163 mg Pb/l from the < 63 mm SF in soils 1B and 1C, respectively, 32 and 37 times more than with the TCLP. The GJST released 55.5 and 56.4% Pb from this fraction in soils 1B and 1C, respectively. In both soils (1B and 1C), lead solubility tended to decrease significantly with an increase in size of particles with the GJST (Tables 5 and 6). The 125–500 mm fractions presented relatively stable leaching values between 25 and 40 mg Pb/l with the GJST, and several times less with the TCLP. On the other hand, the 1000– 2000 mm fraction from site 1C released high concentrations of Pb, 67.3 mg/l with the GJST and 50.2 mg Pb/l with the TCLP. The lead concentration in this fraction was very high (8714 mg/kg). The results for the

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Table 6 Statistical analysis of the results of leached Pb as a function of the total Pb content for the GJST and the TCLP Type of test

Type of regression

Size fraction

n

Equationsa

Correlation coefficient (R)

Normality test

Gastric juice simulation test (GJST)

Linear Linear Linear Linear Linear Linear Linear Multiple linear

1000–2000 mm 500–1000 mm 250–500 mm 125–250 mm 63–125 mm <63 mm All All

8 10 10 10 10 10 58 58

Pb-GJST=4.58+(0.00737Pb-tot) Pb-GJST=13.2+(0.00440Pb-tot) Pb-GJST=14.4+(0.00326Pb-tot) Pb-GJST=15.0+(0.00372Pb-tot) Pb-GJST= 13.8+(0.0217Pb-tot) Pb-GJST= 22.0+(0.0302Pb-tot) Pb-GJST=0.606+(0.0143Pb-tot) Pb-GJST=16.1+(0.0138Pb-tot)-(0.0304SF)b

0.962 0.783 0.653 0.605 0.968 0.929 0.679 0.745

Passed Passed Passed Failed Passed Passed Failed Passed

Toxicity characteristic leaching procedure (TCLP)

Linear Linear Linear Linear Linear Linear Linear Multiple linear

1000–2000 mm 500–1000 mm 250–500 mm 125–250 mm 63–125 mm <63 mm All All

8 10 10 10 10 10 58 58

Pb-TCLP=0.711+(0.00570Pb-tot) Pb-TCLP= 6.12+(0.00470Pb-tot) Pb-TCLP=0.118+(0.00206Pb-tot) Pb-TCLP=9.53-(0.000726Pb-tot) Pb-TCLP=5.24+(0.000792Pb-tot) Pb-TCLP=0.283+(0.00165Pb-tot) Pb-TCLP= 0.167+(0.00275Pb-tot) Pb-TCLP= 4.63+(0.00272Pb-tot)+(0.0111SF)b

0.973 0.932 0.875 0.149 0.167 0.345 0.533 0.671

Passed Passed Passed Passed Failed Failed Failed Failed

a b

Standard deviation for the estimation of Pb-GJST with multiple stepwise regression is 33.6 mg/l. SF, size fraction (the median value of the size fraction class was taken for computation; e.g. 94 for the 63–125 mm fraction).

fraction between 125 and 2000 mm show that total lead content is a more significant parameter than size for these fractions. A simulation was carried out on soils 1B and 1C with the IEUBK model. All the default values were maintained except for lead which was set at 4000 mg Pb/kg for site 1B and at 200 mg Pb/kg for dust. The results indicate that 87% of children aged 0–36 months would exceed the toxicity threshold of 10 mg Pb/dl of blood and that 30% would exceed the value of 23 mg Pb/dl of blood. With soil 1C, the proportion of children affected would rise to 95 and 30% exceeding 10 and 33 mg Pb/dl of blood. Concentrations higher than 200 mg Pb/kg in dust, which are plausible, would make the results even more worrying. However, the TCLP did not show strong contamination in the < 2 mm size fraction in these soils. The GJST is thus a better tool than the TCLP for the detection of lead contamination. Soil 2 contained no particles in the 1–2 mm SF. The < 1 mm SF of soil 2 released 57.6 mg Pb/l with the GJST and 31.8 mg Pb/l with the TCLP (Table 5). The ratio of Pb-GJST/Pb-TCLP is 1.8 and corresponds to the solubilization of 58.1 and 32.1% of the total lead content. The finest fraction always released the most lead, 169 and 25.4 mg Pb/l for the GJST and the TCLP, respectively, for a ratio of 6.7. There was less difference between the two tests for this soil. The only significant difference for this soil is the fact that on average there was 15% PbaSnb(CO3)cOd, compared to 7, 3, 2, and 8% for soil 1A, 1B, 1C and 3 (Table 4). This does not seem sufficient to explain the behaviour of this soil during the GJST and TCLP. For the < 63 mm SF, the leached lead reached a maximum of 74.0% with the GJST. Table 4 shows that 85% of Pb in this fraction was Pb carbonate.

There was a significant increase in the release of lead with the GJST from this soil as the size fraction decreased. The TCLP released from 5.0 to 31.8 mg Pb/l and these concentrations did not seem to be related to the size fraction. Lead solubilization was limited by the pH ( 5) of the TCLP, even though lead contamination in this soil increased very quickly as the SF decreased. Soil 3 contained Pb in slag and lead compounds associated with organic matter and coal residue. The < 2 mm fraction released 22.9 and 0.3 mg Pb/l with the GJST and the TCLP, respectively, for a ratio of 76.3 (Table 5). This soil did not exceed the threshold of 5 mg Pb/l and was not considered problematic according to the results of the TCLP. Based on the GJST, however, lead concentration was rather high in this soil. The results of the IEUBK model [using all the default values and the total lead content of this soil (2457 mg Pb/kg)] indicate that 70 and 11% of children aged 0–36 months would have more than 10 and 25 mg Pb/dl of blood, respectively. However, the TCLP did not detect lead contamination in this soil. The lead released with the GJST was 1526 (22.9/0.015) times higher than the standard for drinking water (0.015 mg Pb/l; USEPA, 1999b).

4. Conclusion This study has shown that the GJST which tries to detect lead problematic soils tends to solubilize more lead from the small particles of a soil than the TCLP. The TCLP leached approximately the same amount of metals from any size fraction, as the TCLP fluid does not have enough free protons (acid) to leach more lead

G. Mercier et al. / Environmental Pollution 118 (2002) 285–296

from small size fractions even if specific surface area and concentration are higher. The TCLP is not able to efficiently solubilize lead from soils as the gastric juice or the GJST can do. The GJST at a pH of 2, with the formation of chlorocomplexes and the presence of an organic acid, solubilizes a good proportion of lead present in soils and seems to be a good indicator of the bioaccessibility of lead in the stomach of children. The TCLP did not detect soils which cause the overpassing of the toxicity theshold of 10 mg of Pb/l of blood (IEUBK model of the USEPA) for a significant proportion of children between 0 and 36 months old. The GJST detected all the problematic soils and was shown to be a better test to rapidly detect lead contaminated soils. The GJST is simple and better because it mimics the pH, the temperature, the kinetics and approximates the chemical composition of the gastric fluid. The use of pepsin in the test could improve the GJST but it would also increase its complexity and probably the variability of the results. The GJST in its present form is, however, a good screening test to detect lead contaminated soils to avoid lead pollution in young children. It should not, however, be used to run precise toxicity studies as no animal model was used to validate its toxicological use.

Acknowledgements This study was funded by the NSERC (Canada) and the FCAR (Quebec). We would like to express our appreciation to Isabel Coulombe, Anne-Marie Leblanc and Myriam Chartier for their technical work. References APHA, 1995. Standards Methods for Examination of Water and Wastewater, 17th Edition. American Public Health Association, Washington DC. Barltrop, D., Meek, F., 1975. Absorption of different lead compounds. Posgraduate Medecine 51, 805–809. Calabrese, E.J., Barnes, R., Stanek III, E.J., Pastides, J., Gilbert, C.E., Veneman, P., Wang, X., Laszity, A., Kostecki, P.T., 1989. Regulation Toxicology and Pharmacology 10, 123–137. Cooper, E.M., Sims, J.T., Cunningham, S.D., Huang, J.W., Berti, W.R., 1999. Chelate-assisted phytoremediation of lead from contaminated soils. Journal of Environmental Quality 28, 1709–1719. Davis, A., Ruby, M.V., Bergstron, P.D., 1992. Bioavaibility of arsenic and lead in soils from the Butte Montana Mining district. Environmental Science and Technology 26 (3), 461–468. Davis, A., Drexler, J.W., Ruby, M.V., Nicholson, A., 1993. Micromineralogy of mine waste in relation to lead bioavaibility from the Butte, Montana. Environmental Science & Technology 27 (7), 1415–1425. Davis, A., Ruby, M.V., Michael, V., Goad, P., Eberle, S., Chryssoulis, S., 1997. Mass balance on surface-bound mineralogic and total lead concentrations as related to industrial aggregate bioaccessibility. Environmental Science and Technology 31, 37–44. Duggan, M.J., Inskip, M.J., Rundle, S.A., Moorcroft, J.S., 1985. Lead in playground dust and the lands of school children. The Science of Total Environment 44, 65–79.

295

Environment Canada, 1992. Guide Me´thodologique de Caracte´risation des Se´diments. Supply and Services Branch. ISBN 0-662-96885-9, 160 pages. Federal Register, 1990. Environmental Protection Agency, United States of America, 55 (61), 11798–11877. Gasser, U., Walker, W., Dahlgren, R.A., Borch, R., Burau, R.G., 1996. Lead release from smelter and mine waste impacted materials under simulated gastric conditions and relation to speciation. Environmental Science and Technology 30 (3), 761–770. Goyer, R.A., 1991. In: Amdur, M.O., Doull, J., Klassen, C.D. (Eds.), Casarett’s and Doull’s Toxicology. Pergamon Press, New York, pp. 623–680. Gue´nard, H., 1991. Physiologie Humaine. Pradel, Paris, France. Guyton, A.C., Hall, J.E., 1996. Textbook of Medical Physiology, 9th Edition. W.B. Saunder, Philadelphia, USA. Healy, M.A., Harrison, P.G., Aslam, M., Davis, S.S., Wilson, C.G., 1982. Lead sulphide and traditional preparations: routes for ingestion, solubility and reactions in gastric fluid. Journal of Clinical Hospital Pharmacy 7, 169–173. Kimbrough, R.D., Falk, H., Stehr, P., Fries, G., 1984. Journal of Toxicology and Environmental Health 14, 47–93. Lanphear, B.P., Matte, T.D., Rogers, J., Clikner, R.P., Dietz, B., Bornschein, R.L., Succop, P., Mahaffey, K.R., Dixon, S., Galke, W., Rabinowitz, M., Farfel, M., Rohde, C., Schartz, J., Ashley, P., Jacobs, D.E., 1998. The contribution of lead-contaminated house dust and residential soil to children’s blood lead level, a pooled analysis of 12 epidemiologic studies. Environmental Research Section A 79, 51–68. (Article vo ER983859). Legiec, I.A., 1997. Pb mobility and extractant optimization for contaminated soil. Environmental Progress 16 (2), 88–92. Marino, M.A., Brica, R.M., Neale, C.N., 1997. Heavy metal soil remediation; the effects of attrition scrubbing on a wet gravity concentration process. Environmental Progress 16, 208–214. MEFQ, 1998. Politique de protection des sols et de re´habilitation des terrains contamine´s. Gouvernement du Que´bec, Ministe`re de l’Environnement et Faune, Annexe 2 tableau 4.2. Mercier, G., Chartier, M., Couillard, D., 1996. Strategies to maximise microbial leaching of lead from sediment bound metal. Water Research 30 (10), 2452–2464. Mice, 1999. Response obtained from the Mice service on the use of the TCLP concerning contaminated soils. See www.epa.gov/sw-846/ mice.htm. Nedwed, T., Clifford, D.A., 1997. A survey of lead battery recycling sites and soil remediation processes. Waste Management 17 (4), 257–269. Option Ame´nagement Inc., 1992. Caracte´risation pre´liminaire de Pointe-Aux-Lie`vres. Rapport pre´sente´ a` la Ville de Que´bec. Ruby, M.V., Davis, A., Nicholson, A., 1994. In situ formation of lead phosphate in soils as a method to immobilize lead. Environmental Science and Technology 28 (4), 646–654. Ruby, M.V., Davis, A., Houston Kempton, J., Drexler, J., Bergstrom, P.D., 1992. Lead bioavailability: dissolution kinetics under simulated gastric conditions. Environmental Science and Technology 26 (6), 1242–1248. Ruby, M.V., Davis, A., Schoof, R., Eberle, S., Sellstone, C.M., 1996. Estimation of lead and arsenic bioavaibility using a physiologically based extraction test. Environmental Science and Technology 30 (2), 422–430. Ruby, M.V., Davis, A., Link, T.E., Schoof, R., Chaney, R.L., Freeman, G.B., Bergstrom, P., 1993. Development of an in vitro sceening test to evaluate the in vivo bioaccessibility of ingested mine-waste lead. Environmental Science and Technology 27 (13), 2870–2877. Ruby, M.V., Schoof, R., Brattin, W., Goldade, M., Post, G., Harnois, M., Mosby, D.E., Casteel, S.W., Berti, W., Carpentier, M., Edwards, D., Cragin, D., Chappell, W., 1999. Advances in evaluating the oral bioavailability of inorganics in soil for use in human health risk assessment. Environmental Science and Technology 33 (21), 3697–3705.

296

G. Mercier et al. / Environmental Pollution 118 (2002) 285–296

Scully Jr., F.E., White, W.N., 1991. Reactions of chlorine monochloramine in the G.I. tract. Environmental Science and Technology 25 (5), 820–828. Sheets, R.C., Bergquist, B.A., 1999. Laboratory treatability testing of soils contaminated with lead and PCBs using particle-size separation and soil washing. Journal of Hazardous Materials 66, 137–150. Sleisenger, M.H., Fordtran, J.S., Scharschmidt, B.F., Feldman, M., 1993. Gastrointestinal Disease, Pathophysiology, Diagnosis and Management, Vol. 1, 5th Edition. W.B. Saunders, Montreal, Canada. USEPA, 1994. Guidance manual for the integrated exposure uptake biokinetic model for lead in children (IEUBK). Prepared by the technical review workgroup for lead for the Office of emergency an remedial response, USEPA. Publication number 9285.7-15-1 EPA 540-R-93-081 PB93-963510, with Document Production Assistance from Envir. Criteria and Assessment Office, USEPA, Research Triangle Park, NC 27711. USEPA, 1999a. Public meeting on the development of new waste leaching procedures, held on 22–23 July 1999 in Crystal City, VA, USA. Available at: www.epa.gov/sw-846/leaching.htm. USEPA, 1999b. United States Environment Protection Agency. Office of Water. Current drinking water standards. Available at: www. epa.gov/OGWDW/wot/appa.html. May 1999.

USEPA, 2001. Method 1312, Synthetic precipitation leaching procedure. Available at: epa.gov/sw-846/1312.pdf. Van Benschoten, J.E., Matsumoto, M.R., Young, W.H., 1997. Evaluation and analysis of soil washing for seven lead-contaminated soils. Journal of Environmental Engineering of the ASCE 123 (3), 217–224. Vick, R.L., 1984. Contemporary Medical Physiology. Addison-Wesley Publishers, Menlo-Park, CA. Williford Jr., C.W., Zhen, L., Wang, Z., Bricka, R.M., 1999. Vertical column hydroclassification of metal-contaminated soils. Journal of Hazardous Materials 66, 15–30. Wixon, B.G., Davies, B.E., 1993. Lead in soil, recommended guidelines. Rapport pre´pare´ pour Society for Environmental Geochemistry and Health ‘‘Lead in soil’’ Task force USEPA. Published by Science Reviews. Xintaras, C., 1992. Analysis Paper: Impact of Lead Contaminated Soil on Public Health. US Department of Health and Human Services Agency for Toxic Substances and Disease Registry, Atlanta Georgia 30333 USA. Zhang, P., Ryan, J.A., 1998. Formation of pyromorphite in anglesite, hydroxyapatite suspensions under varying pH conditions. Environmental Science and Technology 32 (2), 3318–3324.