Pb In Urban Soils Research Articles

Ineffectiveness of phosphorus-containing amendments to reduce Pb bioaccessibility in an urban alkaline soil.

Urban soils contaminated by historical and current anthropogenic activities present an alarming human health risk requiring redress. Federal and state governments continue to lower residential soil lead (Pb) screening standards, which will likely require new risk-based approaches to address urban soil Pb contamination. Phosphorus (P) soil amendments have long been presented as a solution to sequester Pb, thereby reducing exposure risk. In this study, P-containing sources (biosolids incinerator ash, poultry litter, biosolids compost, and triple superphosphate) of varying solubilities were assessed as soil amendments to reduce Pb bioaccessibility and serve as an inexpensive remediation strategy for urban soil. Contaminated soil (1624mg kg-1Pb, pH 7.43) from Cleveland, OH, was treated with the four P-containing soil amendments at a 1:5Pb:P molar ratio and two combination treatments at 1:10Pb:P molar ratio and incubated for 3 months. A batch equilibration analysis was also conducted to assess reduction in in vitro bioaccessible Pb (IVBA Pb). Pb bioaccessibility was evaluated using US EPA Method 1340 at pH 1.5 and the Physiologically Based Extraction Test pH 2.5 at 1 and 3 months. In general, treatments were ineffective in reducing IVBA Pb regardless of IVBA extraction method, incubation duration, batch equilibration analyses, or P source. The results of this study suggest P-containing amendments are not suitable to address Pb exposure in the study soil. Site-specific efficacy testing to determine reductions in IVBA Pb from P-containing amendments should be performed before making recommendations for remediation of Pb-contaminated urban soil.

Unraveling the source(s) and fate of Pb in urban soils and sediments of Ibadan metropolis using lead isotopes.

In this study an attempt was made to determine the source(s) and nature of Pb in environmental media of Ibadan, one of the largest cities in west Nigeria. Seventy-three samples comprising forty stream sediments, twenty-five soils and eight rocks samples were used for the study. Mineralogical compositions of the samples were determined by X-ray diffraction. The elemental constituents were determined using ICP-MS; while the Pb isotopes were determined using Sector-field ICP-MS. Sequential analysis of selected samples was carried out using a modified Tessier's five-step method. The dominant minerals identified were quartz, kaolinite, k-feldspar, and plagioclase. The concentrations (mg/kg) of Pb in soils, sediments, and rocks ranged from 13.00-470.00; 89.00-3288.00 and 2.90-20.30, respectively. The 204Pb, 206Pb, 207Pb, 208Pb ranged from 1.72-47.41; 30.69-779.68; 27.00-664.46 and 65.67-1642.27 in the soils and sediments, respectively, while they ranged from 0.02-0.07; 0.56-2.33; 0.38-1.56 and 1.19-4.13 in the rocks. Further evaluation of Pb concentration in the soils and sediments revealed high to extreme Pb pollution status, while the calculated Pb isotopic ratios (IRs) in the soil and sediments varied from that of the underlying bedrocks. The IRS in soils and sediments were characterized by low (1.161-1.172 and 1.127-1.200, and 2.281-2.444 and 2.276-2.474) 206/207 Pb and 208/207 Pb, while those of the rocks were high (1.456-1.753 and 2.647-3.149), indicating additional anthropogenic sourcing of Pb in the soils and sediments. The analyzed Pb revealed fractions more partitioned in the reactive geochemical phases with the Pb partitioned in the exchangeable (0.11-0.23%), carbonate (9.00-43.58%), reducible (8.32-13.53%) and organic/sulfides (42.78-82.45%) phases. This implies that there may be enhanced mobility of Pb in the environmental samples and ultimately bio-adsorption into living tissues in the environment.

Novel Policies are Required to Reduce Pediatric Lead Exposure from Legacy Lead (Pb) in Soil and Air

In 1925, a U.S. conference on lead (Pb) additives tacitly approved their use in petrol. Over five-decades an exponential increase of air lead occurred from commercial marketing of leaded petrol and the sale of automobiles. The ability to measure microgram quantities of Pb was unavailable to medical researchers until the late 1960s and early 1970s. The clinical application of advanced analytical technology demonstrated that pediatric lead exposure was excessive. Beginning in the mid-1970s, actions were taken to curtail Pb additive and decreases of pediatric lead poisoning coincided with decreased air Pb from leaded petrol use. Exogenous Pb exhaust particles are absorbed through inhalation and ingestion routes of exposure. Exogenous Pb is metabolically mistaken for calcium and stored endogenously in bones, teeth, and other tissues. Endogenous Pb has intergenerational effects. All organs, most notably the nervous system, are affected. Clinical studies indicate that there is no safe level of Pb exposure. A worldwide ban on leaded petrol was achieved on August 30, 2021. Banning leaded petrol corresponded with marked decreases in lead exposure. However, exogenous Pb dust persists in soil as a legacy from the era of leaded petrol. Soil Pb is remobilized into the air. Because of traffic congestion and Pb dust emissions, population centers are of particular concern. An exceedingly strong association exists between soil Pb and blood Pb indicating that at the community-scale Pb dust mitigation is necessary to decrease pediatric Pb exposure. Urban soil Pb and blood Pb studies indicate the risk of excessive exposure from legacy Pb dust in communities is highest where the median soil Pb is ≥ 50 mg/kg. The objective of this article is to demonstrate the practical application of an advanced hand-held analytical instrument to map Pb in children’s playgrounds adjacent to a major traffic corridor. We illustrate soil Pb mapping and then consider mitigation procedures for primary prevention of legacy Pb. Mapping soil Pb provides an informed basis for advising parents and encouraging community mitigation responses for reducing pediatric Pb exposure from legacy Pb dust. The soil health-plant health-animal/human health signaling nexus is compromised by legacy Pb. For the medical pediatric community, the existence of legacy lead requires new policies to address intervention of the soil-air-blood linkages of the Pb exposure pathway.

Legacy of anthropogenic lead in urban soils: Co-occurrence with metal(loids) and fallout radionuclides, isotopic fingerprinting, and in vitro bioaccessibility

Anthropogenic lead (Pb) in soils poses risks to human health, particularly to the neuropsychological development of exposed children. Delineating the sources and potential bioavailability of soil Pb, as well as its relationship with other contaminants is critical in mitigating potential human exposure. Here, we present an integrative geochemical analysis of total elemental concentrations, radionuclides of 137Cs and 210Pb, Pb isotopic compositions, and in vitro bioaccessibility of Pb in surface soils sampled from different locations near Durham, North Carolina. Elevated Pb (>400 mg/kg) was commonly observed in soils from urban areas (i.e., near residential house foundation and along urban streets), which co-occurred with other potentially toxic metal(loids) such as Zn, Cd, and Sb. In contrast, soils from city parks and suburban areas had systematically lower concentrations of metal(loids) that were comparable to geological background. The activities of 137Cs and excess 210Pb, coupled with their correlations with Pb and co-occurring metal(loids) were used to indicate the persistence and remobilization of historical atmospherically deposited contaminants. Coupled with total Pb concentrations, the soil Pb isotopic compositions further indicated that house foundation soils had significant input of legacy lead-based paint (mean = 1.1895 and 2.0618 for 206Pb/207Pb and 208Pb/206Pb, respectively), whereas urban streetside soils exhibited a clear mixed origin, dominantly of legacy leaded gasoline (1.2034 and 2.0416) and atmospheric deposition (1.2004–1.2055 and 2.0484–2.0525). The in vitro bioaccessibility of Pb in contaminated urban soils furthermore revealed that more than half of Pb in the contaminated soils was potentially bioavailable, whose Pb isotope ratios were identical to that of bulk soils, demonstrating the utility of using Pb isotopes for tracking human exposure to anthropogenic Pb in soils and house dust. Overall, this study demonstrated a holistic assessment for comprehensively understanding anthropogenic Pb in urban soils, including its co-occurrence with other toxic contaminants, dominant sources, and potential bioavailability upon human exposure.

Effect of freeze–thaw cycles on soil physicochemical properties and fractions of Pb and Cr in the northeastern Qinghai–Tibet Plateau

Simulation experiments were conducted using soils in the northeastern Qinghai–Tibet Plateau to explore the effects of freeze–thaw cycles on soil physicochemical properties, Pb and Cr distribution, and fraction transformation. Soils were incubated at −15°C for 24 h and at 5°C for 24 h to complete a freeze–thaw cycle. The soil physicochemical properties and fractions of Pb and Cr were analyzed after serial freeze–thaw treatments. The results showed that different freeze–thaw cycles and water content affected soil physicochemical properties and fractions of Pb and Cr to some extent. The cation exchange capacity increased significantly in agricultural and pastoral soils after five freeze–thaw cycles. The sand proportion of soil in an urban area decreased at 60 cycles. Freeze–thaw cycles did not change the functional groups and mineral constituents of the soils. The infrared peaks of soils with different freeze–thaw conditions were very similar. The freeze–thaw treatment influenced the mobility, chemical fractions of Pb and ecological risk in most of the soils. The exchangeable Pb in agricultural and pastoral areas increased from 0.19 to 1.52/0.90% after 5/10 freeze–thaw cycles with 60% water content. The ecological values of Pb in urban soil were 8.32/7.38% higher at 10/15 freeze–thaw cycles compared with the control treatment. Hence, these findings provide useful information on physicochemical properties and fraction transformation of Pb and Cr in soils undergoing freeze–thaw cycles, and offer an additional insight on Pb and Cr behaviors in cold and freezing environments. Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Using historical atmospheric pollution data to prioritize environmental sampling in urban areas

Even when atmospheric particulate matter (PM) pollution declines in urban settings, the residual effects of PM can still be felt by the community. Specifically, PM containing elevated levels of lead (Pb) can accumulate in soils and pose an ingestion/inhalation risk well after deposition because of the relatively immobile chemical nature of Pb. This short communication utilizes a case study of Memphis, TN, where particulate pollution has been reported at high levels. Through conducting time series analysis of atmospheric Pb concentrations, a Pb pollution hot spot in Southwest Memphis is identified as a location where urban soil Pb testing should be focused because of high particulate Pb concentrations in the past. Furthermore, residents in this area are predominantly low income and of ethnic minority (African-American), reiterating previous literature regarding uneven distribution of demographics exposed to pollution in Memphis. Although Pb PM pollution has decreased in recent decades throughout the United States, the use of past Pb air monitoring data in cities can help target specific areas where additional Pb testing may be needed by governments and researchers, particularly where blood Pb level or historical land use data may be limited.

Chemometric Methods to Predict of Pb in Urban Soil from Port Pirie, South Australia, using Spectrally Active of Soil Carbon

ABSTRACTA total of 73 soil samples were initially analyzed for lead (Pb) concentration as an indicator of the environment impact of smelter activity in the Port Pirie, South Australia. Chemometric techniques were used to assess the ability of near-infrared (NIR) reflectance spectroscopy to predict soil Pb using spectrally active soil characteristics such as soil carbon (C). The result indicated a strong linear relationship between log-transformed data of soil Pb and spectral reflectance in the range between 500 and 612 nm with R2 = 0.54 and a low root-mean-square error (RMSEv = 0.38) for the validation mode with an acceptable ratio of performance to deviation and ratio of error range (1.6 and 7.7, respectively). This study suggested that NIR spectroscopy based on auxiliary spectrally active components is a rapid and noninvasive assessment technique and has the ability to determine Pb contamination in urban soil to be useful in environmental health risk assessment.

Lead (Pb) Bioaccessibility and Mobility Assessment of Urban Soils and Composts: Fingerprinting Sources and Refining Risks to Support Urban Agriculture.

While the presence of legacy lead (Pb) in urban soil is well documented, less is known about the bioaccessibility, transport, and exposure pathways of urban soil Pb. We study Pb bioaccessibility in Roxbury and Dorchester, MA, urban gardens to assess exposure risk and identify remediation strategies, applicable locally and in urban gardens across the country. We work in partnership with The Food Project, which brings the goals and perspectives of local farmers to the center of the research process and enables efficient local application of results to reduce Pb exposure. We measure changes in Pb bioaccessibility as a function of growing material, grain size, and Pb source. In comparison to soils, compost has lower total Pb concentrations, has lower Pb solubility in gastric fluid, and limits fine particle resuspension. The mean bioaccessible Pb concentration of compost is 265 mg/kg, nearly an order of magnitude lower than that of soils, and compost contains 14% higher carbon content than soils, which may account for the observed 19% lower Pb bioaccessibility in compost. For all matrices (soil, raised bed fill, and compost) grain sizes <37 μm contain a disproportionate fraction of the total pool of bioaccessible Pb. Furthermore, the isotopic composition of Pb in the size fractions linked with resuspension and elevated blood lead levels is indicative of leaded gasoline and leaded paint even decades removed from the primary deposition of these sources.

A comparative study of metals in roadside soils and urban parks from Hamedan metropolis, Iran

A total of 25 roadside and 25 park soils have been sampled from six major streets and seven urban parks of the city of Hamedan (Iran) and analyzed for Pb and Cd. Metal pollution and spatial distribution maps were carried out using the pollution index(PI), integrated pollution index(IPI) and ordinary kriging with Geographic Information Systems. High levels of Cd and Pb were observed with average concentrations of Cd and Pb in the urban roadside soils being 1.57±0.53, and 164.04±50.08mg/kg, respectively. However, the concentrations in urban park soils (1.16±0.62, and 105.4±46.47mg/kg, respectively), were significantly lower. Vehicle traffic has resulted in a significant enrichment of Cd and Pb in the roadside soils with the highest concentrations found in the city center. The spatial distribution pattern of Cd and Pb in urban soils of Hamedan indicated that the concentration of metals in the central and northern parts of Hamedan is high, due to the human activities. Findings of metals in soils of major streets and urban parks indicated that metal contamination in urban roadside soils was higher than urban parks showing suitability of these soils than urban parks as indicators of metal contamination in urban areas.

Lead isotope and trace element composition of urban soils in Mongolia

Lead (Pb) pollution in and around Ulaanbaatar is of national concern, given that the Mongolian capital is home to nearly half of the country’s entire population. By comparison, Mongolian countryside is a pristine environment because of its sparse population and low industrial activity. The concentration of Pb in urban soils (average of 39.1 mg kg–1) was twice the values found (average 18.6 mg kg–1) in background territories (i.e., Mongolian rural sites). Furthermore, Pb contamination was examined by using Pb stable isotopic composition, and covariance of Pb isotopic ratios showed two groups between rural and urban soils as pristine and disturbed sites. The 206Pb/207Pb ratio, the most prominent fingerprint for Pb pollution, was 1.163–1.185 for the urban whereas values for rural soils (1.186–1.207) were analogue to the regional Pb isotopic signatures. Local coal sources and their combustion products, one of the potential Pb pollution sources in Ulaanbaatar, have significant radiogenic properties in terms of Pb isotopic composition and revealed an average of 1.25 for 206Pb/207Pb and 19.551 for 206Pb/204Pb ratios. Thus, contributions from coal firing activity to Pb pollution lower than it was assumed, and smaller range of these values measured in urban soils may be attributed to the mixing of less radiogenic Pb as a constituent of the leaded gasolines.

Metal(loid) distribution and Pb isotopic signatures in the urban environment of Athens, Greece

Lead concentrations and isotopic compositions of contaminated urban soils and house dusts from Athens, Greece, have been determined to identify possible sources of Pb contamination and examine relationships between these two environmental media. Different soil particle sizes (<2000 μm, <200 μm, <100 μm, <70 μm, <32 μm) and chemical fractions (total, EDTA-extractable and acetic acid-extractable (HAc)) were analyzed for their Pb content and isotopic composition. Metal(loid)s (Pb, Zn, Cu, As, Ni, Cr, Mn, Fe) are significantly enriched in the finest fraction. The Pb isotopic compositions were similar for the different soil particle size fractions and different chemical extractions. The HAc extraction proved to be a useful procedure for tracing anthropogenic Pb in urban soil. The range of 206Pb/207Pb ratios (1.140–1.180) in Athens soil suggests that the Pb content represents an accumulated mixture of Pb deposited from past vehicular emissions and local natural sources. The contribution of anthropogenic Pb to total soil Pb ranged from 36% to 95%. The Pb isotopic composition of vacuum house dusts (206Pb/207Pb = 1.1.38–1.167) from Athens residents is mostly comparable to that of urban soil suggesting that exterior soil particles are transferred into homes. As a result, anthropogenic Pb in house dust from Athens urban environment principally originated from soil particles containing Pb from automobile emissions (former use of leaded gasoline).

Phosphorus Amendment Efficacy for In Situ Remediation of Soil Lead Depends on the Bioaccessible Method.

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccessible Pb in P-treated soils. Two Pb-contaminated soils (790-1300 mg Pb kg), one from a garden and one from a city lot in Cleveland, OH, were incubated in a bench scale experiment for 1 yr. Six phosphate amendments, including bone meal, fish bone, poultry litter, monoammonium phosphate, diammonium phosphate, and triple superphosphate, were added to containers at two application rates. Lead IVBA was assessed using USEPA Method 1340 and three modified versions of this method. Modifications included using solutions with pH 1.5 and 2.5 as well as using solutions with and without 0.4 mol L glycine. Soil amendments were ineffective in reducing IVBA Pb in these soils as measured by pH 1.5 with glycine buffer. The greatest reductions in IVBA Pb, from 5 to 26%, were found using pH 2.5 extractions. Lead mineral results showed several soil amendments promoted Pb phosphate formation, an indicator of remediation success. A significant negative linear relationship between reduction in IVBA Pb and Pb-phosphate formation was found only for pH 2.5 without glycine extraction solution. A modified USEPA Method 1340 without glycine and using pH 2.5 has the potential to predict P soil treatment efficacy and reductions in bioavailable Pb.

A critical physical geography of urban soil contamination

Anthropogenic lead (Pb) is ubiquitous in urban soils given its widespread deposition over the course of the 19th and 20th centuries from a range of point- and non-point sources, including industrial waste and pollution, leaded paint, and automobile exhaust. While soil scientists and urban ecologists have documented soil Pb contamination in cities around the world, such analyses usually focus on proximal mechanisms but rarely consider more distal factors, notably the social processes mediating Pb accumulation in particular places. In this paper, I articulate a critical physical geography of urban soil Pb contamination that considers the dialectical co-production of soil processes and social processes. Using soil Pb contamination in the flatlands of Oakland, California as an empirical case, I integrate conventional quantitative geochemical mapping with theory and qualitative methods regularly employed in urban political ecology to explain the various spatio-temporal processes that bifurcated the city into flatlands and hills, a topography that is as much social as it is physical, and one that is fundamental to differentiated soil Pb concentrations and their disproportionate impact on low-income people of color. I demonstrate how understanding soil contamination through the lens of social metabolism – with particular attention to the materiality of the socio-natural hybrids emerging from processes of capitalist urbanization – can complement conventional analyses, while contributing to a “material politics of place” to support struggles for environmental justice.

Bioavailability-Based In Situ Remediation To Meet Future Lead (Pb) Standards in Urban Soils and Gardens.

Recently the Centers for Disease Control and Prevention lowered the blood Pb reference value to 5 μg/dL. The lower reference value combined with increased repurposing of postindustrial lands are heightening concerns and driving interest in reducing soil Pb exposures. As a result, regulatory decision makers may lower residential soil screening levels (SSLs), used in setting Pb cleanup levels, to levels that may be difficult to achieve, especially in urban areas. This paper discusses challenges in remediation and bioavailability assessments of Pb in urban soils in the context of lower SSLs and identifies research needs to better address those challenges. Although in situ remediation with phosphate amendments is a viable option, the scope of the problem and conditions in urban settings may necessitate that SSLs be based on bioavailable rather than total Pb concentrations. However, variability in soil composition can influence bioavailability testing and soil amendment effectiveness. More data are urgently needed to better understand this variability and increase confidence in using these approaches in risk-based decision making, particularly in urban areas.

Spatial distribution of Pb in urban soil from Port Pirie, South Australia

Abstract Exposure to Lead (Pb) from soil and dust in urban areas continues to threaten human health especially that of children, who are more likely to ingest a higher Pb fraction from contaminated soil. Geostatistical approaches were evaluated for the prediction of soil Pb concentrations. Ordinary kriging (OK) and co-kriging (CoK) were used to predict spatial distributions of both soil Pb concentrations and bioaccessibility. The relative accuracies of the developed predictive models were assessed using of coefficients of determination ( R 2 ) and the root mean square error (RMSE) based on the cross validation method. The accuracy of the final model was evaluated via comparison between predicted and traditional soil measurements. While OK models ( n = 73 ) were unreliable for predicting a Pb concentration surface, correlation between Pb and Zn was a useful mechanism for obtaining better predictions of soil Pb using CoK. The CoK model of log transformed Pb with Zn resulted in the best fitted model ( R 2 = 0.63 ). The percentage relative improvement (RI) for this model was 39% which suggested relatively reliable prediction accuracy. A probability kriging (PK) surface was used to describe the probability of bioaccessibility exceeding a threshold of 17% as an indicator for potential human risk. The areas with highest probability of exceeding the threshold were in agreement with previous risk area divisions related to blood Pb (BPb) levels for children under 5 years of age. The results of this research confirmed that geostatistical methods had the ability to rapidly estimate soil Pb distributions for environmental health risk assessment.

The nature and distribution of Cu, Zn, Hg, and Pb in urban soils of a regional city: Lithgow, Australia

This study investigates the concentration and spatial distribution of Cu, Zn, Hg and Pb in the surface (0–2cm) soils of a regional city in Australia. Surface soils were collected from road sides and analysed for their total Cu, Zn, Hg and Pb concentrations in the <180μm and <2mm grain size fractions. The average metal concentration of surface soils, relative to local background soils at 40–50cm depth, are twice as enriched in Hg, more than three times enriched in Cu and Zn, and nearly six times as enriched in Pb. Median surface soil metal concentration values were Cu – 39mg/kg (682mg/kg max), Zn – 120mg/kg (4950mg/kg max), Hg – 44μg/kg (14,900μg/kg max) and Pb – 46mg/kg (3490mg/kg max). Five sites exceeded the Australian NEPC (1999) 300mg/kg guideline for Pb in residential soils. Strong positive correlations between Cu, Zn and Pb, coupled with the spatial distribution of elevated soil concentrations towards the city centre and main roads suggest traffic and older housing as major sources of contamination. No spatial relationships were identified between elevated metal loadings and locations of past or present industries.

Comparison of plant nutrient and environmental soil tests to predict Pb in urban soils

Most urban soils are not tested for Pb because of the high costs associated with sampling and laboratory analysis of soil contaminants. However, soil testing for plant nutrients is inexpensive and routinely performed for agricultural soils used for food production. The objectives of this study are to determine the ability of 1M HNO3, Mehlich 3, and Modified Morgan soil tests to predict total Pb and other contaminants in urban soils. Total Pb was determined from 65 urban vacant residential lots being considered for urban gardens and food production in Cleveland, OH. Extractable Pb was determined using common soil nutrient test methods Mehlich 3 and Modified Morgan extraction, and a 1M HNO3 extraction. Significant linear regressions between total Pb and Mehlich 3 (r2=0.83), 1M HNO3 (r2=0.92), and Modified Morgan (r2=0.77) in study soils were found. Most commercial and university soil testing labs use Mehlich 3 which could be implemented as a screening tool for soil Pb, Cu, and Zn. The Mehlich 3 soil test is widely used and is relatively inexpensive (<$15). Our results show that total Pb can be conservatively estimated by the following equation Total Pb (mgkg−1)=Mehlich 3 Pb (mgkg−1)×2.

Contamination and source differentiation of Pb in park soils along an urban–rural gradient in Shanghai

Urban soil Pb contamination is a great human health risk. Lead distribution and source in topsoils from 14 parks in Shanghai, China were investigated along an urban-rural gradient. Topsoils were contaminated averagely with 65 mg Pb kg(-1), 2.5 times higher than local soil background concentrations. HCl-extracts contained more anthropogenic Pb signatures than total sample digests as revealed by the higher (207/206)Pb and (208/206)Pb ratios in extracts (0.8613 ± 0.0094 and 2.1085 ± 0.0121 versus total digests 0.8575 ± 0.0098 and 2.0959 ± 0.0116). This suggests a higher sensitivity of HCl-extraction than total digestion in identifying anthropogenic Pb sources. Coal combustion emission was identified as the major anthropogenic Pb source (averagely 47%) while leaded gasoline emission contributed 12% overall. Urbanization effects were observed by total Pb content and anthropogenic Pb contribution. This study suggests that to reduce Pb contamination, Shanghai might have to change its energy composition to clean energy.

The mobility, bioavailability, and human bioaccessibility of trace metals in urban soils of Hong Kong

Abstract Trace metals in soils may pose risks to both ecosystem and human health, especially in an urban environment. However, only a fraction of the metal content in soil is mobile and/or available for biota uptake and human ingestion. Various environmental availabilities of trace metals (Cu, Pb and Zn) in topsoil from highly urbanized areas of Hong Kong to plants, organisms, and humans, as well as the leaching potential to groundwater were evaluated in the present study. Forty selected soil samples were extracted with 0.11 M acid acetic, 0.01 M calcium chloride, 0.005 M diethylenetriaminepentaacetic acid, and simplified physiologically based extraction tests (PBET) for the operationally defined mobilizable, effectively bioavailable, potentially bioavailable, and human bioaccessible metal fractions, respectively. The metals were generally in the order of Zn > Cu ∼ Pb for both mobility (24%, 7.6%, 6.7%) and effective bioavailability (2.8%, 0.9%, 0.6%), Pb (18%) > Cu (13%) > Zn (7.4%) for potential bioavailability, and Pb (59%) ∼ Cu (58%) > Zn (38%) for human bioaccessibility. Although the variations in the different available concentrations of metals could mostly be explained by total metal concentrations in soil, the regression model predictions were further improved by the incorporation of soil physicochemical properties (pH, OM, EC). The effectively bioavailable Zn and Pb were mostly related to soil pH. Anthropogenic Pb in urban soils tended to be environmentally available as indicated by Pb isotopic composition analysis. Combining various site-specific environmental availabilities might produce a more realistic estimation for the integrated ecological and human health risks of metal contamination in urban soils.

Use of local Moran's I and GIS to identify pollution hotspots of Pb in urban soils of Galway, Ireland

Pollution hotspots in urban soils need to be identified for better environmental management. It is important to know if there are hotspots and if the hotspots are statistically significant. In this study identification of pollution hotspots was investigated using Pb concentrations in urban soils of Galway City in Ireland as an example, and the influencing factors on results of hotspot identification were investigated. The index of local Moran's I is a useful tool for identifying pollution hotspots of Pb pollution in urban soils, and for classifying them into spatial clusters and spatial outliers. The results were affected by the definition of weight function, data transformation and existence of extreme values. Compared with the results for the positively skewed raw data, the transformed data and data with extreme values excluded revealed a larger area for the high value spatial clusters in the city centre. While it is hard to decide the best way of using this index, it is suggested that all these influencing factors should be considered until reasonable and reliable results are obtained. GIS mapping can be applied to help evaluate the results via visualization of the spatial patterns. Meanwhile, selected pollution hotspots (extreme values) in this study were confirmed by re-analyses and re-sampling.