Lead Concentrations In Soil Research Articles

THE OCCURRENCE OF LEAD IN SOIL AND VEGETABLES AT A COMMUNITY GARDEN IN OMAHA, NEBRASKA

Abstract – Lead is a persistent and ubiquitous pollutant in urban environments and is of significant importance to public health. Elevated lead concentrations in soil may be due to the use of lead-based paints, emissions from the combustion of leaded gasoline, industrial emissions, waste incineration, and pesticide application. One potential pathway for exposure to lead can be consumption of produce grown in lead-contaminated soil. This may be of increasing concern as urban community gardens experience a resurgence in popularity and demand for locally grown produce increases. For this project, soil and vegetable samples were collected from a community garden with known soil lead contamination. Soil and vegetable samples were evaluated for total lead content using atomic absorption spectroscopy. The concentrations of lead measured in soil ranged from 4 to 574 parts per million (ppm), with an average lead concentration in the growing beds of 128.4 ppm and in the OmaGro compost of 31.5 ppm. Additionally, lead was present in vegetable samples at or below 16.25 ppm.

Hydrocarbon and Toxic Metal Contamination from Tank Installations in a Northwest Greenlandic Village

Contamination from tank installations in the Arctic is an important issue, since tanks are a necessary feature of all communities, and may be a source of local pollution. Soil samples from below and around three tank installations and one reference site in the Northwest Greenlandic village of Tasiusaq were analysed for the total content of hydrocarbons (THC), lead, cadmium and organic content in the soil. Concentrations up to 77,000 mg/kg DW THC were found, mainly as weathered oil products. Elevated levels of lead and cadmium were also found in many of the samples, with concentrations up to 300 and 2 mg/kg DW, respectively. The tank installation areas were contaminated by THC, lead and cadmium compared to the reference site, and parts of the areas were highly contaminated, exceeding the Danish environmental quality criteria. The correlation between lead and cadmium concentrations was significant (p < 0.01), while no correlation existed between THC and organic matter. Small spills from daily use of the tank installations are suggested to be the source of the THC contamination, whereas the lead and cadmium contamination is suggested to originate primarily from the plume of smoke from waste incineration.

The effect of different sulfur doses and forms on changes of soil heavy metals

A three-year field experiment was conducted in North-East Poland. Each year three sulfur fertilization rates in the form of sulphate (S-SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2&amp;ndash;&lt;/sup&gt;) and pure (S&amp;ndash;S&lt;sup&gt;0&lt;/sup&gt;) sulfur were applied: 40, 80, and 120 kg/ha. After the third year of the study, the application of sulfate and elemental sulfur decreased the zinc content of 0&amp;ndash;40 and 40&amp;ndash;80 cm soil layers, as compared with soil sampled before the experiment. Over the entire experimental period, sulfur fertilization had no significant effect on changes in the natural copper content of soil at a depth of 0&amp;ndash;40 and 40&amp;ndash;80 cm. Manganese concentrations remained at a similar level at a soil depth of 0&amp;ndash;40 cm. The manganese content of the 40&amp;ndash;80 cm soil layer was substantially lower than in the 0&amp;ndash;40 cm horizon. An insignificant increase in the lead content of soil was observed. The applied doses of sulfate and elemental sulfur led to an increase in the cadmium content of soil depth of 0&amp;ndash;40 cm. Sulfur fertilization contributed to a decrease in the nickel content of soil. The applied doses of sulfate and elemental sulfur exerted a stronger effect in the 0&amp;ndash;40 cm soil layer than in the 40&amp;ndash;80 cm horizon. &amp;nbsp;

Effects of Long-Term Heavy Metal Contamination on Soil Fungi in the Mediterranean Area

Abstract The lead (Pb) and zinc (Zn) content in soil can qualitatively and quantitatively affect the microbial community and, therefore, the normal functioning of the soil ecosystem. The aim of this study was to assess the effect of long-term Pb and Zn contamination on soil fungi isolated by the dilution plate method, also in relation to vegetal topsoil. We analysed soil samples collected near dominant plant species (Pistacia lentiscus L., Quercus ilex L., Arbutus unedo L., and Phillyrea angustifolia L.) in soils suffering from heavy metal pollution as well as in unpolluted sites. The study area is located in the mining district of Ingurtosu (South-West Sardinia), where the polluted sites were severely contaminated by lead extraction activities that probably began before the Roman era. The obtained data were subjected to multivariate analysis, using Canonical Correspondence Analysis, to determine the relationship between the soil biota and the environmental variables. High concentrations of lead and zinc,...

EFFECT OF NITROGEN FORMS AND RATES ON SOME HEAVY METALS AVAILABILITY AND RICE PRODUCTIVITY UNDER WASTEWATER IRRIGATION

Water shortage in rice cultivation area in Egypt pushed rice farmer to use poor quality water in rice irrigation. Using the correct nitrogen form with the proper rate might be coping with the condition and possible heavy metals in such water. Two field experiments were conducted in 2010 and 2011 seasons at The Farm of Sakha Agriculture Research Station, Kafr-El Sheikh Governorate, Egypt. The soil texture was clayey. EC was 1.5dSm-1. The study aimed to find out the effect of various nitrogen forms; Urea, ammonium nitrate and ammonium sulfate with varying nitrogen levels of 0, 109, 146 and 219 kg N ha-1 on Nickel (Ni), Cadmium (Cd) and Lead (Pb) concentrations in soil, rice straw and rice grain as well as yield and yield components of Giza 178 rice variety under poor quality water .The chemical analysis of irrigation water was as following, Ni 0.28, 0.27, Cd 0.15, 0.17 Pb 0.34, 0.36 mg kg-1, ECw 2.66, 2.71 and pH 8.15 , 8.2 in the first and second seasons, receptively. Results indicated that the tested nitrogen forms and rate significantly affected the concentration of above-mentioned heavy metals, yield and yield components in both seasons. Ammonium sulfate was more efficient than other two nitrogen forms in minimizing heavy metals concentration in soil or rice plants and in enhancing yield and yield components under such poor quality water. The worst nitrogen form was ammonium nitrate regarding heavy metals concentration in plant or soil as well as yield and yield components of rice. Increasing nitrogen rate negatively affected the availability of heavy metals in soil, and their concentration in straw and grain of rice in both seasons. Furthermore, the increase nitrogen level (up to 146 kg ha-1) significantly improved yield and yield components of rice in both seasons.

DETERMINATION OF THE LEVELS OF LEAD IN THE ROADSIDE SOILS OF ADDIS ABABA, ETHIOPIA

Contamination of the roadside soils of Addis Ababa city by lead, most likely originationg from vehicular exhaust, has been investigated. To this end, soil samples were collected from 14 roadside sites; i.e., 2 samples for shorter and 5 samples for longer roads. Determination of lead was carried out on a total of 45 samples and a control sample collected from a relatively remote area of the city, Entoto Mountains, which was assumed to be free of anthropogenic lead sources. The levels of lead in all the samples were determined using flame atomic absorption spectrometer. The concentration of lead obtained from majority of the sample sites surpassed the maximum limit of the metal in soil recommended by WHO (100 μg/g). The average concentrations of lead in the roadside soils were found to be 418.6 ± 3.4 μg/g. Similarly, the concentration of lead in the control soil sample was 18.8 ± 0.5 μg/g. Although at present the lead content of the gasoline used in the country is 0.013 g/L, the use of leaded gasoline during the past decades is thought to be responsible for the high concentration of lead in the roadside soils of Addis Ababa.

Outbreak of Fatal Childhood Lead Poisoning Related to Artisanal Gold Mining in Northwestern Nigeria, 2010

Background: In May 2010, a team of national and international organizations was assembled to investigate children’s deaths due to lead poisoning in villages in northwestern Nigeria.Objectives: Our goal was to determine the cause of the childhood lead poisoning outbreak, investigate risk factors for child mortality, and identify children < 5 years of age in need of emergency chelation therapy for lead poisoning.Methods: We administered a cross-sectional, door-to-door questionnaire in two affected villages, collected blood from children 2–59 months of age, and obtained soil samples from family compounds. Descriptive and bivariate analyses were performed with survey, blood lead, and environmental data. Multivariate logistic regression techniques were used to determine risk factors for childhood mortality.Results: We surveyed 119 family compounds. Of 463 children < 5 years of age, 118 (25%) had died in the previous year. We tested 59% (204/345) of children < 5 years of age, and all were lead poisoned (≥ 10 µg/dL); 97% (198/204) of children had blood lead levels (BLLs) ≥ 45 µg/dL, the threshold for initiating chelation therapy. Gold ore was processed inside two-thirds of the family compounds surveyed. In multivariate modeling, significant risk factors for death in the previous year from suspected lead poisoning included the age of the child, the mother’s work at ore-processing activities, community well as primary water source, and the soil lead concentration in the compound.Conclusion: The high levels of environmental contamination, percentage of children < 5 years of age with elevated BLLs (97%, > 45 µg/dL), and incidence of convulsions among children before death (82%) suggest that most of the recent childhood deaths in the two surveyed villages were caused by acute lead poisoning from gold ore–processing activities. Control measures included environmental remediation, chelation therapy, public health education, and control of mining activities.

Calculation of Remediation Cut-Off Value of Pb-Contaminated Sites Based on the Health Risk

This paper conclude and determine the range of key parameters based on the effects of heavy metal Pb to Human blood-Pb health risk. According to China's reality, Pb levels in air, drinking water are 0.122~1.0 ug/m and 2~10ug/L; ingestion of Pb from food by children of 0~6 years old is 10~25ug/d. Pb cut-off value for residential land soil are calculated with the Integration Exposure Uptake Biokinetic Model (IEUBK). The result shows the Pb cut-off value for residual land is 294.5mg/kg. The result provides a reference for cut-off value of Content of lead in soil, and brings convenience for the research and practice of remediation Pb contamination in soil.

Impacts of mine dump pollution on plant species diversity, composition and structure of a semiarid savanna in Namibia

Effects of mine dump pollution on semiarid savanna vegetation were investigated in Kombat, Namibia. Vegetation structure, species richness, composition and diversity were compared between polluted and control sites. Concentrations of arsenic, chromium, copper, lead and zinc in soils were significantly higher closer to a 99-year-old mine dump than in a control site and exceeded internationally recommended guidelines by as high as 11 times. Mine dump pollution has significantly reduced woody plant densities, species richness and diversity in the affected area due to disappearance of pollution-sensitive species and preponderance of tolerant ones. Species composition and structure of vegetation close to the mine dump significantly changed, possibly due to negative impacts of heavy metals on recruitment as pollution-sensitive species died off, whereas tolerant species invaded the vacated ecological niches. Ordination analyses confirmed a strong pollution gradient, with measured heavy metals accounting for 57.3% of the observed variation in species data, suggesting that other factors are also important determinants in the area. It is recommended that the mine dump and its surrounds should be rehabilitated and regular monitoring should be carried out to remedy the situation and arrest further pollution of the surrounding environment.

Remediating Lead, Zinc, Cadmium and Arsenic Contaminated Steel Smelting Site with Hydrochloric Acid and Sodium Hydroxide

A-two step soil washing experiment was conducted to search an effective washing technique for the remediation of the contaminated soil from a steel smelting site. Our results indicated that 0.5M of hydrochloric acid alone could reduce soil cadmium concentration to lower than 1 mg kg-1, 1M of hydrochloric acid alone could reduce soil lead concentration to lower than 140 mg kg-1, 2M of hydrochloric acid combined with 0.2M of sodium hydroxide could reduce soil zinc concentration to lower than 200 mg kg-1 and reduce soil arsenic concentration to lower than 20 mg kg-1, the washed soil could be safely reused according to the national exhibition land quality standards of grade A.

The origin of lead in the organic horizon of tundra soils: Atmospheric deposition, plant translocation from the mineral soil or soil mineral mixing?

Knowledge of the anthropogenic contribution to lead (Pb) concentrations in surface soils in high latitude ecosystems is central to our understanding of the extent of atmospheric Pb contamination. In this study, we reconstructed fallout of Pb at a remote sub-arctic region by using two ombrotrophic peat cores and assessed the extent to which this airborne Pb is able to explain the isotopic composition ( 206Pb/ 207Pb ratio) in the O-horizon of tundra soils. In the peat cores, long-range atmospheric fallout appeared to be the main source of Pb as indicated by temporal trends that followed the known European pollution history, i.e. accelerated fallout at the onset of industrialization and peak fallout around the 1960s–70s. The Pb isotopic composition of the O-horizon of podzolic tundra soil ( 206Pb/ 207Pb = 1.170 ± 0.002; mean ± SD) overlapped with that of the peat ( 206Pb/ 207Pb = 1.16 ± 0.01) representing a proxy for atmospheric aerosols, but was clearly different from that of the parent soil material ( 206Pb/ 207Pb = 1.22–1.30). This finding indicated that long-range fallout of atmospheric Pb is the main driver of Pb accumulation in podzolic tundra soil. In O-horizons of tundra soil weakly affected by cryoturbation (cryosols) however, the input of Pb from the underlying mineral soil increased as indicated by 206Pb/ 207Pb ratios of up to 1.20, a value closer to that of local soil minerals. Nevertheless, atmospheric Pb appeared to be the dominant source in this soil compartment. We conclude that Pb concentrations in the O-horizon of studied tundra soils – despite being much lower than in boreal soils and representative for one of the least exposed sites to atmospheric Pb contaminants in Europe – are mainly controlled by atmospheric inputs from distant anthropogenic sources.

Lead concentration in soil from an old mining town

Lead concentration in soils has been measured in Vetagrande, an old mining town located at the state of Zacatecas in Mexico. Eighty nine soils samples were analyzed using Energy Dispersive X-ray Fluorescence. The lead concentrations were treated with the Kriging method in order to estimate the lead concentration distribution in the studied area. Pb levels in soils were from 8 to 7730 lg kg -1 , where 28.1% of soil samples have less than 400 lg kg -1 , 71.9% is above 400 l gk g -1 which is the maximum level recommended by the EPA for residential use of soil. Lead concentration measured around public sites represent a risk of lead intake in the population.

Environmental Lead Pollution and Elevated Blood Lead Levels Among Children in a Rural Area of China

We investigated environmental lead pollution and its impact on children's blood lead levels (BLLs) in a rural area of China. In 2007, we studied 379 children younger than 15 years living in 7 villages near lead mines and processing plants, along with a control group of 61 children from another village. We determined their BLLs and collected environmental samples, personal data, and information on other potential exposures. We followed approximately 86% of the children who had high BLLs (> 15 μg/dL) for 1 year. We determined factors influencing BLLs by multivariate linear regression. Lead concentrations in soil and household dust were much higher in polluted villages than in the control village, and more children in the polluted area than in the control village had elevated BLLs (87%, 16.4 μg/dL vs 20%, 7.1 μg/dL). Increased BLL was independently associated with environmental lead levels. We found a significant reduction of 5 micrograms per deciliter when we retested children after 1 year. Our data show that the lead industry caused serious environmental pollution that led to high BLLs in children living nearby.

Incorporation of lead into calcium carbonate granules secreted by earthworms living in lead contaminated soils

The influence of soil organisms on metal mobility and bioavailability in soils is not currently fully understood. We conducted experiments to determine whether calcium carbonate granules secreted by the earthworm Lumbricus terrestris could incorporate and immobilise lead in lead- and calcium-amended artificial soils. Soil lead concentrations were up to 2000 mg kg −1 and lead:calcium ratios by mass were 0.5–8. Average granule production rates of 0.39 ± 0.04 mg calcite earthworm −1 day −1 did not vary with soil lead concentration. The lead:calcium ratio in granules increased significantly with that of the soil ( r 2 = 0.81, p = 0.015) with lead concentrations in granules reaching 1577 mg kg −1. X-ray diffraction detected calcite and aragonite in the granules with indications that lead was incorporated into the calcite at the surface of the granules. In addition to the presence of calcite and aragonite X-ray absorption spectroscopy indicated that lead was present in the granules mainly as complexes sorbed to the surface but with traces of lead-bearing calcite and cerussite. The impact that lead-incorporation into earthworm calcite granules has on lead mobility at lead-contaminated sites will depend on the fraction of total soil lead that would be otherwise mobile.

Evaluation of the Contribution of Lead in Soil to Lead in Dust at Superfund Sites

ABSTRACT The concentration of lead in indoor dust is a key parameter in the Integrated Exposure Uptake Biokinetic (IEUBK) model used by the U.S. Environmental Protection Agency (USEPA) to evaluate risks to children from lead in soil. The default assumption is that the concentration of lead in indoor dust is 70% of the concentration of lead in outdoor soil. This report reviews the basis of this assumption, and compares the assumption to data obtained at mining/smelting Superfund sites in USEPA Region 8. Data for lead concentrations measured in both indoor dust and outdoor soil at a number of different properties at nine different Superfund sites were fit to a linear model (Cdust = K0 + Ksd·Csoil). Based on ordinary linear regression, values of Ksd ranged from 0.04 to 0.34. Values of Ksd estimated using a simple method to account for measurement errors yielded values from 0.04 to 0.35. These findings indicate that the concentration of lead in dust at mining/smelting sites in Region 8 is usually not as large as the IEUBK default assumption indicates. Use of the default is likely to be protective, but will likely result in an overestimation of childhood exposure and risk from lead in soil.

Effect of Calcium on Growth Performance and Essential Oil of Vetiver Grass (Chrysopogon zizanioides) Grown on Lead Contaminated Soils

The aim of this study was to investigate effect of calcium on growth, survival, essential oil yield, and chemical compositions of vetiver grass grown on lead contaminated soils. Calcium in form of CaCO3 (0, 2000, 4000, 6000 mg Ca kg−1) was added to river sand soils containing 4000 mg Pb kg−1 dry soil. Results showed that, in the absence of calcium treatment, no plants survived after 2 weeks of cultivation, while the rest grew well to the end of the experimental period (42 weeks). Calcium treatments generally resulted in a slight decrease in biomass. Interestingly, an increase in calcium over 2000 mg kg−1 did not result in a decrease in accumulation of lead in vetiver roots and shoots. The levels of lead in roots and shoots under calcium treatments were around 2000 and 90 mg kg−1 dry weight, respectively. The addition of CaCO3 did not improve vetiver essential oil yield and chemical composition compared to the control. A level of applied CaCO3 about half of the lead concentration in soils was sufficient to improve vetiver growth and survival, and accumulate high concentrations of lead in the roots. This finding can be applied for re-vegetation of lead contaminated soils using vetiver.

Assessment and Remediation of Lead Contamination in Senegal

Background. This paper describes the impact of improper used lead-acid battery (ULAB) handling and disposal. A specific case study is presented describing the field assessment and remediation of lead contamination in a community in Senegal where at least 18 children died from lead poisoning.Objectives. The assessment and remediation process utilized to address the Senegal lead contamination has been used as a model approach to solving used lead-acid battery (ULAB) contamination in other economically depressed communities worldwide. This paper addresses exterior soil remediation with a future paper planned to address interior remediation and blood lead level declines as a marker for project success.Materials &amp; Methods. A comprehensive field program was developed and implemented to delineate the extent of soil lead contamination. The lead-impacted soil was the source of elevated blood lead levels due to direct ingestion (children playing in impacted soil), dust migration and impacted soil tracking into homes, shops and schools. Soil lead concentrations in surface soil and at depth were determined during several site assessments. The soil lead data were collected in conjunction with blood lead testing and collection of dust wipe samples for laboratory analysis. Soil lead data were also collected during and after soil excavation activities to document remediation success.Results. The data showed widespread soil contamination throughout the community. Surface soil exhibited lead concentrations as high as approximately 20% lead (200,000 mg/kg or parts-per-million as compared to the U.S. standard of 400 mg/kg). Blood lead levels in children were highly elevated and reached as high as 613.9 &amp;mu;g/dL (as compared to the U.S. standard of 10 &amp;mu;g/dL). Bulk dust samples from inside residences were as high as 26,889 mg/kg (2.7% lead). Post-excavation soil testing demonstrated that the majority of impacted soil was removed and the exterior exposure pathway was significantly reduced.Conclusions. Lead contamination in an economically depressed community resulted in the deaths of at least 18 infants. A coalition of local community members, local and federal government agencies, and international non-governmental organizations was able to develop and implement a comprehensive assessment and remediation strategy specifically focused on minimizing future risks to the local population with minimal disruption. The implemented soil removal plan resulted in site remediation without population relocation, spanning just over two years, and being completed under the budget of USD 200,000.

Kontaminácia zemiakov ťažkými kovmi a ich vplyv na tvorbu fenolových zlúčenín

Increased content of cadmium and lead in soil was manifested by their increased concentration in potato tubers in such range that contents were several times higher (Cd 0.106-0.357, Pb 0.318-0.483 mg.kg-1 FM) then the limit value. Increased content of zinc was not manifested by increased content in tubers of potatoes (Zn 4.939- 6.868 mg.kg-1 FM). Content of total phenolics (TP) in potato samples of Hontiansky and Banskoštiavnický region was in the range of 263.59-920.38 mg.kg-1 of dry material. Exceeded content of cadmium and lead in potato tubers had statistically significant effect on total phenol producing, but on the other hand relation between contents of Zn and TP in potato tubers was not statistically confirmed. Also positive correlation between TP and antioxidant activity contents was statistically confirmed.

Fractionation of lead in soil by isotopic dilution and sequential extraction

Environmental contextThe chemical reactivity of lead in soil is difficult to assess and depends on both soil conditions and the origins of the lead. This paper tests the combined application of lead isotopic techniques and chemical extraction against our understanding of lead fractionation in soils. Possibly against expectation, it appears that the ‘reactivity’ of lead can be high and yet there is tentative evidence that the original source of the metal affects its fractionation in soil, even after long contact times. Abstract‘Reactivity’ or ‘lability’ of lead is difficult to measure using traditional methods. We investigated the use of isotopic dilution with 204Pb to determine metal reactivity in four soils historically contaminated with contrasting sources of Pb, including (i) petrol-derived Pb, (ii) Pb/Zn minespoil, (iii) long-term sewage sludge application and (iv) 19th century urban waste disposal; total soil Pb concentrations ranged from 217 to 13 600 mg kg–1. A post-spike equilibration period of 3 days and suspension in 5.0 × 10–4 M ethylenediaminetetraacetic acid provided reasonably robust conditions for measuring isotopically exchangeable Pb. However, in acidic organic soils a dilute Ca(NO3)2 electrolyte may be preferable to avoid mobilisation of ‘non-labile’ Pb. Results showed that the reactive pool of soil Pb can be a large proportion of the total soil lead content but varies with the original Pb source. A comparison of isotopic exchangeability with the results of a sequential extraction procedure showed that (isotopically) ‘non-labile’ Pb may be broadly equated with ‘residual’ Pb in organic soils. However, in mineral soils the ‘carbonate’ and ‘oxide-bound’ Pb fractions included non-labile forms of Pb. The individual isotopic signatures of labile and non-labile Pb pools suggested that, despite prolonged contact with soil, differences between the lability of the original contaminant and the native soil Pb may remain.

Lead distribution and its potential risk to the environment: Lesson learned from environmental monitoring of abandon mine

There are many abandon and existing mines (tin, lead and zinc) in the mountainous areas of Thailand. Toxic elements including heavy metals such as lead (Pb), cadmium (Cd) and arsenic (As) have been released and transported from the mining sites to the adjacent landscape. In Thong Pha Phum District, Kanchanaburi Province, Thailand Pb contamination in the vicinity of the mine has occurred which could lead to potential health problems in downstream communities. To better understand current status of Pb contamination and accumulation in the surrounding environment and potential health impact, surface sediment, soil and plant samples were collected seasonally from representative monitoring sites along the aquatic track or flow regime. Potential health risk was determined using hazard quotient (HQ) as an index for local inhabitants who consume rice. Environmental monitoring illustrated that Pb concentrations in the surface sediment was as high as 869.4 mg kg−1 dry weight and varied differently among stations sampled. Lead content in agricultural soil ranged between 137.8 to 613.5 mg kg−1 dry weight and was inversely proportion to the distance from the point source. Moreover Pb was transported from the point source to down hill areas. At the highly polluted monitoring stations (S1, S2, and S3), concentrations of Pb exceeded the maximum allowable concentration for Pb in agricultural soil (300 mg kg−1) by 1.7–2 times. The Pb in soil was primarily associated with Fe/Mn oxides bound fraction (46–56%) followed by the organic bound fraction (25–30%). Lead uptake by plant varied and was species dependent. However root and tuber crops like cassava (19.92 mg Pb kg−1 dry weight) and curcumin (3.25 mg Pb kg−1 dry weight) could have removed Pb from the soil which suggest growing root crops in Pb contaminated soils should be avoided. However Cd, a co-contaminant at one of monitored stations (S4) yielded rice grain with Cd exceeding the maximum allowable concentration suggesting some potential health risk (HQ = 5.34) if people consume rice grown at this station. Overall result shows a low risk associated with Pb release into the environment.