Human Health Risk Assessment Model Research Articles

Distribution Characteristics and Health Risk Assessment of Metals in Drinking Water Sources from the Luhun Reservoir

In order to investigate the distribution characteristics and the human health risks of 12 metals in drinking water sources from the Luhun Reservoir, Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, and Zn concentrations in 46 water samples collected from the reservoir in 2016 were measured and analyzed. The health risks caused by metals were assessed by using a human health risk assessment model. The results showed that the maximum concentration of Al (200.27 μg·L-1) and all concentrations of Mo (151.42-170.69 μg·L-1) in drinking water from the Luhun Reservoir exceeded the Environmental Quality Standards for Surface Water (GB 3838-2002) and Standards for Drinking Water Quality (GB 5749-2006) by 4.35% and 100%, respectively. A distinct spatial heterogeneity was found in the metal distribution, and the region with the highest metals concentrations was located southwest (upstream) and northeast (downstream) of the reservoir. The results of a health risk assessment indicated that children had greater health risks than adults. The health risks for metals through drinking were all higher than the values caused by dermal contact. Carcinogenic risks caused by Cr and As exceeded the maximum allowance levels (5×10-5 a-1) by 100% and 3.80%, respectively, and Cr accounted for 85% of the total carcinogenic risks. The non-carcinogenic risks of the metals (10-12-10-7 a-1) decreased in the order of Al > Mo > Cu > Pb > Ni > Hg > Fe > Zn > Mn, which had levels two to seven orders of magnitude lower than the maximum allowance levels.

Ecological risk assessment and carcinogen health risk assessment of arsenic in soils from part area of the Daye City, China

Soils in four sampling sites from part area of the Daye City were collected. Concentrations of arsenic (As) in soils in sampling sites were detected by Atomic Fluorescence Spectrometry, ecological risk was calculated by potential ecological risk index (RI) and human health risk was measured by human health risk assessment model established by USEPA. The results showed that, the total content of As in soils in Daye was decreased in the order of S4 (66.58 mg/kg)>S2 (44.73 mg/kg)>S3 (34.86 mg/kg) >S1 (21.84 mg/kg), concentrations in all sampling sites were higher than background values of Hubei Province. The potential risk and human health risk were decreased in the order of S4>S2>S3>S1 and S4>S3>S2>S1, respectively. Specially, S1, S2 and S3 were at low potential ecological risk while S4 was at moderate ecological risk. But there was no carcinogenic risk for human exposure to As in soil in Daye.

Bioaccessibility and human health risk assessment of lead in soil from Daye City

Lead (Pb) in soil from 4 sampling sites of Daye City was studied. Bioaccessibilities of Pb in soil were determined by the method of simplified bioaccessible extraction test (SBET). Since traditional health risk assessment was built on the basis of metal total content, the risk may be overestimated. Modified human health risk assessment model considering bioaccessibility was built in this study. Health risk of adults and children exposure to Pb based on total contents and bioaccessible contents were evaluated. The results showed that bioaccessible content of Pb in soil was much lower than its total content, and the average bioaccessible factor (BF) was only 25.37%. The hazard indexes (HIs) for adults and children calculated by two methods were all lower than 1. It indicated that there were no no-carcinogenic risks of Pb for human in Daye. By comparing with the results, the average bioaccessible HIs for adults and children were lower than the total one, which was due to the lower hazard quotient (HQ). Proportions of non-carcinogenic risk exposure to Pb via different pathways have also changed. Particularly, the most main risk exposure pathway for adults turned from the oral ingestion to the inhalation.

Levels, Sources, Markers and Health Risks of Heavy Metals in PM2.5 Over a Typical Mining and Metallurgical City of Central China

To investigate the pollution characteristics, sources and health risk assessment of various elements in PM2.5 of Huangshi city, 54 samples were collected from March 2012 to February 2013. The composition and characteristic of sixteen elements (Mg, Al, Ca, Ti, Cr, Mn, Cu, Zn, V, Fe, As, Pb, Cd, Co, Ni and W) were analyzed by high-sensitivity X-ray fluorescence (XRF). The result showed that the annual mean concentration of PM2.5 was 104.4 μg/m3, far exceeding the secondary level of Ambient Air Quality Standard of China (annual average limit 35 μg/m3). Element W has the highest annual concentration, followed by Zn, Pb and As. Compared with the concentration limit of National Ambient Air Quality Standard of China, Cd and As in Huangshi were 4.3 times and 32.8 times higher, respectively, than national standard. The concentration of most elements has distinct seasonal characteristic which is higher in winter and lower in summer. Enrichment factor (EF) analysis indicates that W, Fe, Cd, As, Pb, Zn, Cu, Cr, Co and Ni are extremely enriched in PM2.5, Ca, Mg and Mn are highly enriched, and V is significant enriched. EF of Ti is less than 2, suggesting minimal pollution. Positive matrix factorization (PMF) analysis indicates that Ca, Ti and Al are associated with fugitive dust, and As is associated with coal-fired industrial activity. W, Cr, Cd, V and Ni are originated from chemical and metallurgical industry activities. Pb, Zn, Cu and Mg are derived from vehicle emissions. The results of the human health risk assessment model show that As may pose great non-carcinogenic risk to children and adults. Cr and As have a higher carcinogenic risk for adults, and Cr has a higher carcinogenic risk for children, and other toxic metals are in relatively safe range.

Health risk assessment of exposure to ambient concentrations of benzene, toluene and xylene in Pretoria West, South Africa

Benzene, toluene and xylene (BTX) are part of the volatile organic group of pollutants and are seen as international environmental priority air pollutants that can constitute a threat to public health. This study assessed the non-carcinogenic and carcinogenic risks of exposure to BTX in an industrial area located in Pretoria West, South Africa. The study comprised two parts, namely ambient air monitoring and the application of a Human Health Risk Assessment (HHRA) model. The study included sampling data for the 2014 calendar year (January – December). Sampling frequency were hourly samples of ambient concentrations of BTX. Estimate of the possible non-carcinogenic risk of BTX and carcinogenic risk of benzene were determined using the hazard quotient (HQ) and lifetime cancer risk (LCR) respectively. Annual average concentration (µg/m3) of BTX was 0.9 ± 0.9, 2.2 ± 2.5 and 0.8 ± 0.6, respectively, with higher concentrations during winter months. The HQ indicated no likelihood of adverse health effects on children and adults. The HQ of exposure to BTX were <1 for both children (0.094 µg/m3) and adults (0.38 µg/m3). The LCR of exposure to benzene among children (4.4 × 10−7) as well as adults (1.8 × 10−6) was lower than those stipulated by regulatory organizations.

Investigation and health risk assessment of heavy metals in soils from partial areas of Daye city, china

Heavy metals (Cu and Pb) in four sampling sites from parts areas of Daye city were collected. Concentrations of Cu and Pb in soils in sampling sites were detected, the enrichment degree was measured by geo-accumulation index, and the human health risks were calculated by applying the human health risk assessment model. The results show that the concentrations of Cu and Pb of soils in some areas are much more than Daye City, Hubei Province soil background value. The concentration of Cu and Pb in Xiaganwan soil sample has a higher value and the concentration of Cu (110.17 mg·kg-1) exceeds the soil environmental quality standards. The values of Igeo of Cu and Pb in the soil in some areas of Daye city are 1 except Xiaganwan sample is 2. For human health risk assessment, the non-cancer risk of Cu in three routes of exposure is less than Pb. The non-cancer risk both adults and children are less than 1 and show a general trend of HQ in oral ingestion exposure pathway > HQ in inhalation exposure pathway>HQ in skin contact exposure pathway. It will not cause significant non-carcinogenic health effects on the human body.

Distribution Characteristics and Health Risk Assessment of Heavy Metals in Surface Water Around Electroplating Factories

To investigate the distribution characteristics and the human health risks of heavy metals in surface water samples, 30 samples were collected around electroplating factories of Machong, Shatian, Humen, Changan and Dalingshan towns in Dongguan city, 8 heavy metals(As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) contents were measured and analyzed by using multivariate statistical analysis method and human health risk assessment model. The results showed that the maximum concentrations of Cr, Pb and the average concentration of Hg exceeded Environmental Quality Standards for Surface Water(GB 3838-2002, Grade Ⅲ), the concentrations of Cr, Cu, Hg, Ni, Zn and Pb during rainy season were all higher than that those during dry season. Multivariate statistical analysis indicated that Cd, Cr, Cu, Ni and Zn mainly originated from the contaminated electroplating factories, Pb and Hg were mainly affected by the traffic sources, and As was significantly correlated with natural sources. Health risk assessment result of surface water indicated that heavy metal pollution would lead to high health risks especially for children, and the health risks of heavy metals through drinking pathway were 2-3 orders of magnitude higher than the values caused by dermal contact pathway. Moreover, carcinogenic risks caused by Cr and As were higher than the maximum allowance levels (5×10-5 a-1), and non-carcinogenic risks of the heavy metals (10-10-10-7 a-1) decreased in the order of Pb > Ni > Cu > Hg > Zn, which were 4-5 orders of magnitude lower than the maximum allowance levels.

Groundwater nitrate pollution and human health risk assessment by using HHRA model in an agricultural area, NE China

In order to learn the pollution circumstance of groundwater nitrate detailedly in Songnen Plain of Northeast China and estimate its potential risk to human health of local residents, a total of 389 groundwater samples were collected in 2014 and studied from residential areas and public water supply wells in 11 cities and counties in southeastern of Songnen Plain. The analysis results showed that the spatial distributions of main chemical components in groundwater had great variations with statistical concentrations in the order of TDS> HCO3> Ca> NO3> Cl> Na> SO4> Mg> K> NH4> NO2. As for NO3, it ranged from less than 0.02mg/L to 497mg/L with an average value of 39.46mg/L indicating an obviously anthropogenic pollution. Even more than 32% of the samples exceeded the Grade III threshold (20mg/L of N) according to China's standard. The results obtained from principal component analysis showed that high NO3 concentration could be attributed to human activities, especially the excessive use of chemical fertilizers in agriculture. Further, a human health risk assessment (HHRA) model derived from the US Environmental Protection Agency (USEPA) was applied to estimate the potential health risk of groundwater nitrate considering both drinking water and dermal contact pathways. The results indicated that potential health risks of adult males and females within about 60% of the area were at the acceptable level, while those within about 40% were beyond the acceptable level. The area at the acceptable level for children covered 49% of the total area while the same value for infants was 37%. The NO3 concentration in southeast and northeast of the study area was the highest so that residents in these regions were at the highest health risk. In conclusion, risk levels for different crowds in the study area varied obviously, generally in the order of infants> children> adult females> adult males, and the potential health risks of residents, especially minors and rural residents, should cause enough attention both from the society and the academic community.

Applicability of drinking water treatment residue for lake restoration in relation to metal/metalloid risk assessment.

Drinking water treatment residue (DWTR), a byproduct generated during potable water production, exhibits a high potential for recycling to control eutrophication. However, this beneficial recycling is hampered by unclear metal/metalloid pollution risks related to DWTR. In this study, the pollution risks of Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn due to DWTR application were first evaluated for lake water based on human health risk assessment models and comparison of regulatory standards. The risks of DWTR were also evaluated for sediments on the basis of toxicity characteristics leaching procedure and fractionation in relation to risk assessment code. Variations in the biological behaviors of metal/metalloid in sediments caused by DWTR were assessed using Chironomus plumosus larvae and Hydrilla verticillata. Kinetic luminescent bacteria test (using Aliivibrio fischeri) was conducted to analyze the possibility of acute and chronic detrimental effects of sediment with DWTR application. According to the obtained results, we identify a potential undesirable effect of DWTR related to Fe and Mn (typically under anaerobic conditions); roughly present a dosage threshold calculation model; and recommend a procedure for DWTR prescreening to ensure safe application. Overall, managed DWTR application is necessary for successful eutrophication control.

Distribution and health risk assessment of dissolved heavy metals in the Three Gorges Reservoir, China (section in the main urban area of Chongqing).

The Three Gorges Project (TGP) is the largest hydropower station ever built in the world. A better understanding of the concentrations of heavy metals in the aquatic environment of the Three Gorges Reservoir (TGR) is crucial for national drinking water security and sustainable ecosystem development. To thoroughly investigate the impact of heavy metals on water quality after the impoundment to the maximum level of 175m in the TGR, the concentrations of the dissolved heavy metals (Cr, Cu, Zn, Cd, Pb, As) were measured in April and August 2015, by inductively coupled plasma mass spectrometry (ICP-MS). (1) Except Zn and Pb, most of the heavy metal concentrations in the water of the TGR reached the level of the National Surface Water Environmental Quality Standards (GB3838-2002) I of China, revealing that the water quality of the TGR was good overall. (2) There were significant positive correlations among the concentrations of Cu, As, and Cd, revealing that they may exhibit similar geochemical behaviors. (3) The spatial distribution of the heavy metal concentrations was diverse and complex. The Zn concentration obviously increased in the rainy season from upstream to downstream in the Yangtze River, while the other heavy metals exhibited no significant changes in their concentrations. The distribution characteristics of the heavy metal concentrations on both sides and the middle of the river were different at different sites. (4) The health risk of the six elements was assessed through a human health risk assessment (HHRA), and the assessment results were lower than the maximum acceptable risk level designed by the US EPA and International Commission on Radiological Protection (ICRP). The HHRA model in the aquatic environment revealed that the risk of non-carcinogenic heavy metals (Cu, Zn, and Pb) was at a negligible risk level of 10-11∼10-9a-1. At all the study sites, the risk of carcinogenic heavy metals (Cr, Cd, and As) was higher than the risk of non-carcinogenic heavy metals. As was the most important risk factor, followed by Cr. The results of this study hold great significance for a timely understanding of the changing water quality for affected departments to ensure the health of the residents in the TGR area.

Assessment of pollution levels and human health risk of heavy metals in dust deposited on Yerevan’s tree leaves (Armenia)

The total concentrations of Cd, As, Pb, Cr, Ni, Co, Zn, Cu, Ag, Hg, and Mo were determined in the atmospheric dust of the city of Yerevan by atomic absorption spectrometry (AAnalyst PE 800). Heavy metal pollution levels were evaluated by calculating geo-accumulation (I geo ) and summary pollution (Zc) indices. Potential human health risk was assessed using the United States Environmental Protection agency’s human health risk assessment model. The results show that mean contents of all elements tested except Ni and Cr were substantially higher than local geochemical background values. According to the I geo , Yerevan territory is strongly-to-extremely polluted by As, Ag, Hg, Mo, and Cd. The Zc assessment indicated that very high pollution was detected in 36 % of samples, high in 32 %, average in 12 %, and low in 20 %. The health risk assessment revealed a non-carcinogenic risk (HI >1) for children at 13 samplings sites and for adults at one sampling site. For children the risk was due to elevated levels of Mo, Cd, Co, and As, while for adults, only Mo. Carcinogenic risk (>1:1,000,000) of As and Cr via ingestion pathway was observed in 25 and 14 samples, respectively. This study, therefore, is the base for further detailed investigations to organize problematic site remediation and risk reduction measures.

Risk assessment of bioaccessible trace elements in smoke haze aerosols versus urban aerosols using simulated lung fluids

Abstract Smoke-haze episodes, caused by uncontrolled peat and forest fires, occur almost every year in the South-East Asian region with increased concentrations of PM2.5 (airborne particulate matter (PM) with diameter ≤ 2.5 μm). Particulate-bound trace elements (TrElems), especially carcinogenic and toxic elements, were measured during smoke haze as well as non-haze periods in 2014 as they are considered to be indicators of potential health effects. The bioaccessibilities of 13 TrElems were investigated using two types of simulated lung fluids (SLFs), Gamble's solution and artificial lysosomal fluid (ALF), instead of the commonly used leaching agent (water). The dissolution kinetics was also examined for these TrElems. Many TrElems showed higher solubility in SLFs, and were more soluble in ALF compared to the Gamble's solution. Cu, Mn and Cd were observed to be the most soluble trace elements in ALF, while in Gamble's solution the most soluble trace elements were Cu, Mn and Zn. The dissolution rates were highly variable among the elements. Health risk assessment was conducted based on the measured concentrations of TrElems and their corresponding toxicities for three possible scenarios involving interactions between carcinogenic and toxic TrElems and SLFs, using the United States Environmental Protection Agency (USEPA) human health risk assessment model. The cumulative cancer risks exceeded the acceptable level (1 in a million i.e. 1 × 10−6). However, the estimation of health quotient (HQ) indicated no significant chronic toxic health effects. The risk assessment results revealed that the assessment of bioaccessibility of particulate-bound TrElems using water as the leaching agent may underestimate the health risk.

Assessment of regional human health risks from lead contamination in Yunnan province, southwestern China.

Identification and management the 'critical risk areas' where hotspot lead exposures are a potential risk to human health, become a major focus of public health efforts in China. But the knowledge of health risk assessment of lead pollution at regional and national scales is still limited in China. In this paper, under the guidance of 'sources-pathways-receptors' framework, regional human health risk assessment model for lead contamination was developed to calculate the population health risk in Yunnan province. And the cluster and AHP (analytic hierarchy process) analysis was taken to classify and calculate regional health risk and the decomposition of the regional health risk in the greatest health risk region, respectively. The results showed that Yunnan province can be divided into three areas. The highest health risk levels, located in northeastern Yunnan, including Kunming, Qujing, Zhaotong region. In those regions, lead is present at high levels in air, food, water and soil, and high population density which pose a high potential population risk to the public. The current study also reveals that most regional health risk was derived from the child receptors (age above 3 years) 4.3 times than the child receptors (age under 3years), and ingestion of lead-contaminated rice was found to be the most significant contributor to the health risk (accounting for more than 49 % health risk of total). This study can provide a framework for regional risk assessment in China and highlighted some indicators and uncertainties.

Human Health Risk Assessment Model of Organic Pollution in Groundwater: Shijiazhuang Industrial Zone

Abstract:In this study, a risk‐based management model is developed and applied to an industrial zone. The models proposed by the United States Environmental Protection Agency and Han Bing have been improved by adding a residual ratio of volatile organic compounds (VOC) after boiling and deleting the related parameters in half‐life. Using this improved model, an integrated process was used to assess human health risk level in the study area. Compared with water quality analysis, the results highlight the importance of applying an integrated approach for decision making on risk levels and water protection. The results of this study demonstrated that: (1) Compared with these permissible level standards in China (GB 3838–2002) and National Primary Drinking Water Regulations of the United States, the residents' daily life had not been affected by the groundwater in this area (except for relative bad water quality of HB3–4 and HB3–6); (2) The typical detected organic contaminants of all groundwater samples were chloroform, carbon tetrachloride, trichloroethylene and tetrachloroethene, and the pollution sources were mainly industrial sources by preliminary investigations; (3) As for groundwater, the non‐carcinogenic risk values of all samples do not exceed the permissible level of 1.0 and the carcinogenic risk values are relatively lower than the permissible level of 1.00E‐06 to 1.00E‐04; (4) Drinking water pathway of trichloroethylene and tetrachloroethylene mainly contribute to increasing the health risk of residents' in study areas; (5) In terms of non‐carcinogenic risk and carcinogenic risk, the health risk order for drinking water pathway and dermal contact pathway was: drinking water pathway &gt; dermal contact pathway.

Determination of the bioaccessibility of chromium in Glasgow soil and the implications for human health risk assessment

The Unified Bioaccessibility Method (UBM), which simulates the fluids of the human gastrointestinal tract, was used to assess the oral bioaccessibility of Cr in 27 Glasgow soils. These included several contaminated with Cr(VI), the most toxic form of Cr, from the past disposal of chromite ore processing residue (COPR). The extraction was employed in conjunction with the subsequent determination of the bioaccessible Cr by ICP-OES and Cr(VI) by the diphenylcarbazide complexation colorimetric procedure. In addition, Cr(III)-containing species were determined by (i) HPLC-ICP-MS and (ii) ICP-OES analysis of gel electrophoretically separated components of colloidal and dissolved fractions from centrifugal ultrafiltration of extracts. Similar analytical procedures were applied to the determination of Cr and its species in extracts of the < 10 μm fraction of soils subjected to a simulated lung fluid test to assess the inhalation bioaccessibility of Cr. The oral bioaccessibility of Cr was typically greater by a factor of 1.5 in the ‘stomach’ (pH ~ 1.2) compared with the ‘stomach + intestine’ (pH ~ 6.3) simulation. On average, excluding two COPR-contaminated soil samples, the oral bioaccessibility (‘stomach’) was 5% of total soil Cr and, overall, similar to the soil Cr(VI) concentration. Chromium(VI) was not detected in the extracts, a consequence of pH- and soil organic matter-mediated reduction in the ‘stomach’ to Cr(III)-containing species, identified as predominantly Cr(III)-humic complexes. Insertion of oral bioaccessible fraction data into the SNIFFER human health risk assessment model identified site-specific assessment criteria (for residential land without plant uptake) that were exceeded by the soil total Cr (3680 mg kg -1) and Cr(VI) (1485 mg kg -1) concentration at only the most COPR-Cr(VI)-contaminated location. However, the presence of measurable Cr(VI) in the < 10 μm fraction of the two most highly Cr(VI)-contaminated soils demonstrated that inhalation of Cr(VI)-containing dust remains the most potentially harmful exposure route.

Development of Total Health Risk Analysis System for Integrated Environmental Management

P-783 Abstract: Health risk assessment is a process of estimating the qualitative and quantitative effects that might occur when a person is exposed to environmental hazards. The ultimate objective of risk assessment is to provide rational and scientific information for risk management, especially in the areas of environmental policy making and regulatory control. The objectives of this study were to develop available ‘system software’ in health risk assessment for multimedia and multipathways scenarios and to serve it as Decision Support System (DSS) for effective management of environmental risk in municipal and industrial areas in Korea. We planed to develop prototype of system software in the first phase (2001∼2003) and generic type of that including Geographical Information System (GIS) in the second phase (2004∼2006). The human health risk assessment model for multimedia and multipathways scenarios could estimate health risks from human exposure considering environmental multimedia (ambient air, indoor air, surface water, drinking water, and ground soil) and 12 multipathways. We constructed the several databases such as physiological, chemical and toxicological properties for 58 chemicals (PAHs, VOCs, pesticides, and metals), exposure parameters of Korean, and population information for study areas. The modeling areas were seven main metropolitan areas and ten industrial complexes in Korea. This model could evaluate individual and population risk and would be supported the various exposure parameters for Korean. For the validation of heath risk model, we measured concentration for residents in the several areas, and estimated the total human exposure and health risk for the subjects. The model predictions generally agreed with the estimated within an accuracy factor (predicted level/measured level) of 10 for PAHs, VOCs and POPs chemicals. We were assessed to 7 metropolitan cities and 10 industrial areas in Korea. Priority for excess cancer risk in metropolitan cities was Seoul>Daegu≫Ulsan>Incheon>Busan>Gwangju≫Daejeon. In industrial areas, priority for excess cancer risk was Daegue Seongseo and Daegue Dye≫Ulsan>Sinpyeong Jangnim>Cheongju>Siwha-Banwol>Yecheon>Gumi> Deajeon≫Jeonju. The PAHs were the predominant pollutants through all exposed route (inhalation, ingestion and dermal contact) in all medium (ambient air, surface water and soil). The carcinogenic metals (cadmium, chromium, lead) and VOCs in ambient air were the predominant pollutants. The hazard quotients (HQ) for non-cancer pollutants were less than 1 for all chemicals in all subject areas. The health risk assessment model can prevent environmental accidents induced chemicals used in local regions. Priority for health risk would be listed in terms of regions, media, and chemicals based on the health risk assessment model. The health risk assessment model is available identification and management for environmental pollutants and can be more efficiently and reasonably resource allocation more for risk management.

A framework for assessing the impact of land use policy on community exposure to air toxics

Our research focuses on the linkage between land use planning policy and the spatial pattern of exposure to air toxics emissions. Our objective is to develop a modeling framework for assessment of the community health risk implications of land use policy. The modeling framework is not intended to be a regulatory tool for small-scale land use decisions, but a long-range planning tool to assess the community health risk implications of alternative land use scenarios at a regional or subregional scale. This paper describes the development and application of an air toxic source model for generating aggregate emission factors for industrial and commercial zoning districts as a function of permitted uses. To address the uncertainty of estimating air toxics emission rates for planned general land use or zoning districts, the source model uses an emissions probability mass function that weights each incremental permitted land use activity by the likelihood of occurrence. We thus reduce the uncertainty involved in planning for development with no prior knowledge of the specific industries that may locate within the land use district. These air toxics emission factors can then be used to estimate pollutant atmospheric mass flux from land use zoning districts, which can then be input to air dispersion and human health risk assessment models to simulate the spatial pattern of air toxics exposure risk. The model database was constructed using the California Air Toxics Inventory, 1997 US Economic Census, and land assessment records from several California counties. The database contains information on more than 200 air toxics at the 2-digit Standard Industrial Classification (SIC) level. We present a case study to illustrate application of the model. LUAIRTOX, the interactive spreadsheet model that applies our methodology to the California data, is available at http://www2.bren.ucsb.edu/~mwillis/LUAIRTOX.htm.

Heterogeneity of cadmium concentration in soil as a source of uncertainty in plant uptake and its implications for human health risk assessment

The major route of exposure of humans to the toxic element cadmium (Cd) is via the consumption of vegetables homegrown on Cd contaminated soil. It is well known that soil pH is one of the main soil properties controlling bioavailability of Cd in plants. This is acknowledged in human health risk assessment models that incorporate pH dependant concentration factors (CF=plant Cd/soil Cd). However, variation in spatial heterogeneity of nutrients and heavy metals in soil can have a profound effect on plant performance and uptake of nutrients and heavy metals. Here we show for lettuce (variety Crispino) that variation in plant-scale heterogeneity of Cd in soil affects bioavailability and hence CF by a factor of 2. Plant yield is also significantly affected. This has important implications for both human health risk assessment, as variation in CF affects predicted exposure, and for phytoremediation where an optimal combination of plant yield and contaminant accumulation is required.

EFFECT OF CULTURE CONDITIONS PRIOR TO EXPOSURE ON CADMIUM CYTOTOXICITY IN PRIMARY RAT HEPATOCYTES

Primary rat hepatocytes area useful research tool for direct investigation of hepatotoxic effects of chemicals or drugs at the cellular level. USEPA's reevaluation of current human health risk assessment models for thetoxicmetal cadmium has identified a need for the development of new models that include in vitro toxicity and kinetic data. The EC50 for cadmium obtained in rat hepatocyte cultures in 96-well plates (EC50 [96]=3.2 0.8muM) was found to be significantly different from that obtained in 6-well cultures (EC50 [6]=14.8+/-0.7muM). When medium depth in 96-well plates was adjusted to reflect the same depth as that in 6-well plates prior to, during, and following cadmium exposure, an EC50 was observed that was similar to that obtained in 6-well plates (EC50 [96*]=13.2+/-0.9muM). Hepatocytes incubated in 96-well plates with various depths of culture medium, from 1 mm (34muL/well)to 6 mm (200muL/well), exhibited a significant decrease in viability and attached cell protein with greater medium depths. As...