Revisiting Dust and Soil Ingestion Rates Based on Hand-to-Mouth Transfer

Soil ingestion rates calculated using a tracer-based mass balance approach may carry considerable study errors, insensitivities, and “artefacts” of analysis that result in significant uncertainty. These same soil ingestion rates are often used as surrogates for dust ingestion rates. Therefore, a more direct and mechanistic method was developed to estimate soil and dust ingestion rates. The soil and dust ingestion rates were calculated using measures of: particle loading to indoor surfaces; fraction transferred to the hands; hand surface area; fraction of hand surface area that may be mouthed or contact food; frequency of hand-to-mouth events, amount dissolved by saliva; and exposure time. Adapted specifically for the Canadian context, estimated mean indoor dust ingestion rates range from 2.2 mg/d for teenagers to 41 mg/d for toddlers; mean soil ingestion rates range from 1.2 mg/d for seniors to 23 mg/d for children. Combined soil and dust ingestion rates ranged from 3.8 mg/d for seniors to 61 mg/d for toddlers. These ingestion rates are lower than values adopted by most agencies. These ingestion rates are mechanistic, can be adjusted on a site-specific basis, can be modified into an hourly rate and are presented as a more realistic alternative to traditional mass balance approaches.

[Supplementary materials are available for this article. Go to the publisher's online edition of Human and Ecological Risk Assessment to view the free supplementary files.]     

Contamination and health risk assessment of trace elements in soil at play centers of urban low-income settings

Abstract

Young children are considered critical receptors of potentially toxic trace elements (PTEs) by non-dietary ingestion of contaminated soil. The study assessed the potential enrichment of soil and the health risk of PTEs to 471 children less than seven years via non-dietary soil ingestion at six Early Childhood Development Centers (ECDCs) in urban low-income settings. The total concentrations of PTEs were determined by ICP-AES after wet acid digestion. The extent of soil contamination with PTEs and their source apportionment were assessed by the enrichment factor (EF). The US-EPA risk assessment model was used to determine the risk of PTE exposure by children. Multivariate statistical analyses and the EF suggested anthropogenic origin of PTEs in playgrounds and indoors, especially Cd and Pb from atmospheric deposition. Indoor floor dust at ECDCs was enriched (significant to extreme) with PTEs of anthropogenic origin imported from the outside environment. Children at the six ECDCs were not at significant non-carcinogenic risk of PTEs in soil and dust through non-dietary ingestion. The study setting is typical of urban child play centers in low-income countries which needs regular risk assessment and the enforcement of legislation in order to reduce the exposure of children to PTEs.     

Ecological Risk Assessment of Radiological Exposure to Depleted Uranium in Soils at a Weapons Testing Facility

The potential for unacceptable risks to biota from radiological exposure to depleted uranium (DU) in soils was evaluated at two sites where DU weapons testing had been conducted in the past. A screening risk assessment was conducted to determine if measured concentrations of DU-associated radionuclides in site soils exceed radionuclide levels considered protective of biota. While concentrations of individual radionuclides did not exceed acceptable levels, total radionuclide concentrations could result in potentially unacceptable doses to exposed biota. Thus, a receptor-specific assessment was conducted to estimate external and internal radiological doses to vegetation and wildlife known or expected to occur at the sites. Wildlife evaluated included herbivores, omnivores, and top-level predators. Internal dose estimates to wildlife considered exposure via fugitive dust inhalation and soil and food ingestion; root uptake was the primary exposure route evaluated for vegetation. Total doses were compared with acceptable dose levels of 1.0 and 0.1 rad/day for vegetation and wildlife, respectively, with potentially unacceptable risks indicated for doses exceeding these levels. All estimated doses were below or approximated acceptable levels, typically by an order of magnitude or more. These results indicate that current levels of DU in soils do not pose unacceptable radiological risks to biota at the sites evaluated.     

What proportion of household dust is derived from outdoor soil?

This report estimated the amount of outdoor soil in indoor dust in the Calabrese et al. (1989) children soil ingestion study via the use of statistical modelling. The estimate used data on outdoor soil and indoor dust in the homes of 60 children with eight tracer elements (Al, Ba, Mn, Si, Ti, V, Y, and Zr). The model estimated that 31.3% of indoor dust had an origin of outdoor soil. Based on a previous report (Stanek and Calabrese, 1992) on differential soil from dust ingestion in the Calabrese et al. (1989) study and the data of the present analysis, the median outdoor soil ingestion of the Calabrese et al. (1989) study should be revised downward by 35%. For the three most reliable tracers, the median soil ingestion estimates would be reduced from 29 to 19 mg/d for Al, 55 to 36 mg/d for Ti, and 16 to 10 mg/d for, Zr.     

Soil Ingestion Distributions for Monte Carlo Risk Assessment in Children

Monte Carlo environmental risk assessment requires estimates of the exposure distributions. An exposure of principal concern is often soil ingestion among children. We estimate the long-term (annual) average soil ingestion exposure distribution using daily soil ingestion estimates from children who participated in a mass-balance study at Anaconda, MT. The estimated distribution is accompanied by uncertainty estimates. The estimates take advantage of developing knowledge about bias in soil ingestion estimates and are robust. The estimates account for small particle size soil, use the median trace element estimate for subject days, account for the small sample variance of the median estimates, and use best linear unbiased predictors to estimate the cumulative long term soil ingestion distribution. Bootstrapping is used to estimate the uncertainty of the distribution estimates. The median soil ingestion is estimated as 24?mg/d (sd = 4?mg/d), with the 95 percentile soil ingestion estimated as 91?mg/d (sd = 16.6?mg/d). Strategies are discussed for use of these estimates in Monte Carlo risk assessment.     

Soil ingestion in children: Outdoor soil or indoor dust?

Soil ingestion estimates may play a prominent role in exposure estimation for risk assessments involving tightly bound soil contaminants such as dioxin, PCBs, and lead in soil. Since contamination is often localized to specific areas, the relative contribution of ingested soil due to outdoor soil and indoor dust may have a large impact on the risk assessment. This article examines data on 64 preschool children over 2 weeks to estimate the relative contribution of ingested soil from outdoor soil and indoor dust. Four principal methodological approaches are developed and presented to form the estimates, and their relative strengths and weaknesses are discussed.

The four approaches differ in their assumptions and their ability to detail differences in ingestion source. Two approaches (i.e., duration correlation method — approach 1 and group tracer ratio method — approach 2) were used that can only estimate the average ingestion source, where averages are calculated over subjects and weeks. Both of these approaches have sufficient limitations to preclude confidence in the resulting estimates.

The final two approaches (approach 3 — individual tracer ratio method and approach 4 — multiple statistical model method) were able to characterize ingestion source for individual subject‐weeks and offered more plausible estimates of soil ingestion. Greater emphasis is placed on approach 3 since it was biologically plausible and conceptually straightforward. Approach 3 indicated that 49.2% ± 29.2% of the residual fecal tracers were estimated to be of soil origin. These findings, which represent the first quantitative differentiation of soil vs. dust ingestion, have considerable application for a variety of environmental settings requiring exposure assessment.     

Health risk assessment on heavy metals in urban street dust of Tianjin based on trapezoidal fuzzy numbers

The aims of this article were to investigate heavy metals concentrations in urban street dust of Tianjin, to examine spatial variations of heavy metals pollution, and to assess their health risk to local populations. Urban street dust samples were collected from 144 typical crossroads in an urban area of Tianjin. Levels of heavy metals were determined by atomic absorption spectrophotometer analyzer. Given comprehensive consideration of the complexity and uncertainty of health risk assessment, trapezoidal fuzzy number was introduced to assess the health risk of heavy metals in the urban street dust of Tianjin. The results showed that the pollution of heavy metals in the urban street dust of Tianjin was serious. The relatively serious metal pollution tended to be located in the center, north, northeast, and southeast of the study area. The research indicated that heavy metals in street dust had caused non-cancer hazard to children but had not caused non-cancer or cancer hazard to adults. The direct ingestion of dust via hand-mouth contact behaviors was the major exposure pathway for health risk.     

Estimation of Sediment Ingestion Rates Based on Hand-to-Mouth Contact and Incidental Surface Water Ingestion

There is a lack of scientifically justified approaches for assessing sediment ingestion rates of people exposed to contaminated sediments. Consequently, a method was developed to estimate sediment ingestion rates from: (1) hand-to-mouth contact with sediments and (2) incidental ingestion of surface water containing suspended sediments. In the case of hand-to-mouth contact, a mechanistic approach was used based on established principles and assumptions previously used for estimation of soil and dust ingestion rates. A key modification of the approach was to account for greater adherence of sediments to hands as compared to soil and dusts. For estimation of sediment ingestion from surface water contact, a method was developed that considered the unique aspects of suspended sediments. The analysis indicated that hand-to-mouth contact is the dominant pathway for ingestion of sediment. When people use aquatic areas for recreational purposes, the analysis has indicated that mean sediment ingestion rates may range from 18 to 72 mg/h for various receptor age groups. For sites where people spend more than 1 h per day on a consistent basis in direct contact with sediments, the results indicate that sediment ingestion rates may be greater than those typically assumed in Canadian human health risk assessment guidance for soils.     

Assessment of potential health risk of heavy metals in soils from a rapidly developing region of China

Soil heavy metal contamination is a major environmental concern, and health risk associated with heavy metals is not fully explored. A combination of spatial analysis and Monte Carlo simulation was successfully used to identify the possible sources and health risk of cadmium (Cd), arsenic (As), mercury (Hg), lead (Pb), chromium (Cr), and copper (Cu) in soils collected from a rapidly developing region of China. It was found that mean concentrations of Cd (0.17 mg/kg ), As (8.74 mg/kg ), Hg (0.15 mg/kg ), Pb (27.28 mg/kg ), and Cu (33.32 mg/kg ) were greater than the soil background values. Accumulation and spatial variability of heavy metals were significantly affected by anthropogenic activities and soil properties. The risk assessment indicated that non-carcinogenic risk was not significant. However, 95% of the total cumulative carcinogenic risk of children was greater than 1E-05, implying high potential carcinogenic risk with As and Pb representing the major contributors. Ingestion of heavy metals in the soils was the main exposure pathway compared with the inhalation and the dermal exposure. Concentration of heavy metals in the soils, particulate emission factor, and dermal exposure ratio were the major parameters affecting health risk. This study highlights the importance of assessment of soil direct exposure health risk in studying heavy metal exposures.     

Widespread environmental contamination in agricultural soils and human health risk at the vicinity of an oil refinery site

In this research, carcinogenic and non-carcinogenic human health risks due to polycyclic aromatic hydrocarbons (PAHs) were investigated via three exposure pathways: accidental ingestion of soil, dermal contact of soils, and contaminated vegetable ingestion. To determine the contaminant concentrations in soil, samples were collected from areas adjacent to the Tehran oil refinery, located in Shahr-e-Ray city, Iran. Analyses of the samples indicated that the average of PAHs concentration in the soil samples were greater than clean-up level guidelines. Cancer risk of contaminants due to ingestion of cultivated vegetables that are sold in Tehran markets was significant in comparison with other exposure pathways. Moreover, the total cancer risk for 5th percentile, 95 upper confidence limit, and 95th percentile concentration of contaminants were 5.69E-04, 8.78E-02, and 2.13E-01, classifying the site as having a significant cancer risk potential. Furthermore, non-carcinogenic health risk analyses for the contaminants demonstrated hazard index of less than 1. Remediation of the soils is highly recommended to eliminate the potential cancer risks and prevent the contamination of the food chain for approximately 10 million Tehran residents.     

Probabilistic Sensitivity Analysis of Public Health Risk Assessment from Contaminated Soil

Recently, there has been a growing trend toward using stochastic (probabilistic) methods in ecological and public health risk assessment. These methods are favored because they overcome the problem of compounded conservatism and allow the systematic consideration of uncertainty and variability typically encountered in risk assessment. This article demonstrates a new methodology for the analysis of uncertainty in risk assessment using the first-order reliability method (FORM). The reliability method is formulated such that the probability that incremental lifetime cancer risk exceeds a predefined threshold level is calculated. Furthermore, the stochastic sensitivity of this probability with respect to the random variables is provided. The emphasis is on exploring the different types of probabilistic sensitivity obtained through the reliability analysis. The method is applied to a case study given by Thompson et al. (1992) on cancer risk resulting from dermal contact with benzo(a)pyrene (BaP)-contaminated soils. The reliability results matched those of the Monte Carlo simulation method. On average, the Monte Carlo simulation method required about 35 times as many function evaluations as that of FORM to calculate the probability of exceeding the target risk level. The analysis emphasizes the significant impact that the uncertainty in cancer potency factor has on the probabilistic modeling results compared with other parameters.     

Pollution characteristics and health risk assessment of potentially toxic elements in school playground soils: A case study of Lagos,Nigeria

Abstract

Soil samples were collected in February 2014 from 25 school playgrounds in Lagos, Nigeria to assess the potential adverse effects of the exposure of children to potentially toxic element (PTE). In each of the playgrounds, about 500?g of bulked soil samples were collected, dried, sieved, acid digested, and analyzed by inductively coupled plasma mass spectrometry (ICP‐MS). Results showed that soils studied were characteristically unpolluted as the average PTE concentration at each site did not exceed the soil guideline values. Considering the pollution assessment tools employed, some soil samples showed some form of anthropogenic input from PTE. Health risk assessment was employed to assess PTE exposure from ingestion, inhalation, and dermal contact. Result indicated that the highest risk is associated with ingestion followed by dermal contact and inhalation. For non‐carcinogenic effects, exposure to school playground soils poses no threat to children as the overall value of hazard index is less than the safe level of 1. For carcinogenic effects, only Cr and Ni were considered and were below the threshold of 1?×?10^–6. This study has demonstrated that minimal risk arises from the investigated playgrounds and that regular monitoring is required to keep the PTE contents low in soils to avoid risk to human health.

Abbreviations: SH, school playground; PTE, potentially toxic elements     

Contamination level and human health hazard assessment of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in street dust deposited in Mahshahr,southwest of Iran

Mahshahr has a strategic position and is considered as industrial hub of Iran. Selected heavy metals and polycyclic aromatic hydrocarbons (PAHs) contamination and health risk, and the mineralogical composition of street dust from Mahshahr were investigated. Results indicated that geology is the main determinant of the dust mineralogical composition. Calculated enrichment factor (EF) and principal component analysis (PCA) showed that Pb, Hg, Zn, and Cu accumulations are greatly influenced by anthropogenic sources including traffic and industry. High heavy metals content poses great ecological risk in the study area and exposure doses revealed that ingestion is the main exposure route to street dust, especially for children in residential/commercial areas. It was found that the total amount of PAHs (∑PAHs) varies from 161 to 1996 µg/kg, dominated by four-ring PAHs. Diagnostic ratios and PCA showed that both petrogenic and pyrogenic sources of PAHs in Mahshahr street dust and traffic play important roles in this respect. Furthermore, toxic equivalents and incremental lifetime cancer risk of PAHs in street dust indicated a high potential carcinogenic risk for inhabitants mainly via dermal contact and ingestion pathways particularly for outdoor workers in industrial use scenario. Finally, distribution maps of total hazard index of heavy metals and cancer risk of PAHs indicated the most impacted zones for different groups and use scenarios.     

A Caution for Monte Carlo Risk Assessment of Long Term Exposures based on Short-Term Exposure Study Data

Monte Carlo risk assessments commonly take as input empirical or parametric exposure distributions from specially designed exposure studies. The exposure studies typically have limited duration, since their design is based on statistical and practical factors (such as cost and respondent burden). For these reasons, the exposure period studied rarely corresponds to the biologic exposure period, which we define as the time at risk that is relevant for quantifying exposure that may result in health effects. Both the exposure period studied and the biologic exposure period will often differ from the exposure interval used in a Monte Carlo analysis. Such time period differences, which are often not accounted for, can have dramatic effects on the ultimate risk assessment. When exposure distributions are right skewed and/or follow a lognormal distribution, exposure will usually be overestimated for percentiles above the median by direct use of exposure study empirical data, since biologic exposure periods are generally longer than the exposure periods in exposure assessment studies. We illustrate the effect that biologic exposure time period and response error can have on exposure distributions, using soil ingestion as an example. Beginning with variance components from lognormally distributed soil ingestion estimates, we illustrate the effect of different modeling assumptions, and the sensitivity of the resulting analyses to these assumptions. We develop a strategy for determining appropriate exposure input distributions for soil ingestion, and illustrate this using data on soil ingestion in children.     

Assessing the Bioavailability and Risk from Metal-Contaminated Soils and Dusts

Exposure to contaminated soil and dust is an important pathway in human health risk assessment. Physical and chemical characteristics and biological factors determine the bioaccessibility/bioavailability of soil and dust contaminants. Within a single sample, contamination may arise from multiple sources of toxic elements that may exist as different species that impact bioavailability. In turn, the bioaccessibility/bioavailability of soil and dust contaminants directly impacts human health risk. Research efforts focusing on development and application of in vitro and in vivo methods to measure the bioaccessibility/bioavailability of metal-contaminated soils have advanced in recent years. The objective of this workshop was to focus on developments in assessing the bioaccessibility/bioavailability of arsenic-contaminated soils, metals’ contamination in urban Canadian residences and potential children's exposures to toxic elements in house dust, an urban community-based study (i.e., West Oakland Residential Lead Assessment), bioavailability studies of soil cadmium, chromium, nickel, and mercury and human exposures to contaminated Brownfield soils. These presentations covered issues related to human health and bioavailability along with the most recent studies on community participation in assessing metals’ contamination, studies of exposures to residential contamination, and in vitro and in vivo methods development for assessing the bioaccessibility/bioavailability of metals in soils and dusts.     

Risk-Based Zoning Strategy for Soil Remediation at an Industrial Site

After determining at an early stage of the project that the future land use of this New Jersey chemical manufacturing site remain industrial in nature, the site was zoned according to risk. The chemicals of concern (COCs) at the site included relatively low levels of mono- and polynuclear aromatic hydrocarbons, chlorinated aliphatics, as well as other volatile and semivolatile compounds. Direct human exposure scenarios were the key to the mitigation of risks related to soils because the groundwater migration pathway was already interrupted using groundwater recovery. A focused remedial strategy was developed to ensure that the exposure pathways (inhalation, ingestion, and dermal contact) are alleviated and the remedial measures are protective to the workers operating and/or maintaining the site. The risk evaluation process included a preliminary risk assessment (Tier 1) based on a comparison with pertinent soil cleanup criteria, a prioritization analysis to rank zones, chemicals and pathways of concern, and an application of the Risk Based Corrective Action (RBCA) approach (Tier 2) for construction worker exposure scenario. The risk assessment identified selected areas that would benefit from remedial actions. Prioritization Analysis classified the site into five high-priority (comprising 97% of the total health-based risk), three medium-priority (contributing to remaining 2 to 3% of the risk), and adequately protected areas. The boundaries and volumes of affected areas were delineated based on confirmatory soil sampling and statistical analyses. The remedial technologies selected for the site have achieved appropriate reduction in risk to comply with all State regulations and include (in addition to the institutional controls): ??Capping the site where only immobilesemivolatile contaminants are present ??Excavation and on-site treatment of the soils impacted by volatile organic com pounds through ex situ low temperature desorption, or alternative “biopile” treatment and natural attenuation, and ??Excavation and off-site disposal of limited volumes of soils This risk-based, integral approach helped identify the real significance of contamination present at the site and facilitated the development of suitable and adequate remedies. Had not it been for this approach, the mere comparison with soil cleanup criteria would have unnecessarily resulted in denoting all areas as nuisance contributors, and thus requiring some actions. New Jersey Department of Environmental Protection (NJDEP) has approved this approach and contributed to its accomplishment.     

Analysis and Portrayal of Uncertainty in a Food-Web Exposure Model

The results of quantitative risk assessments are key factors in a risk manager's decision of the necessity to implement actions to reduce risk. The extent of the uncertainty in the assessment will play a large part in the degree of confidence a risk manager has in the reported significance and probability of a given risk. The two main sources of uncertainty in such risk assessments are variability and incertitude. In this paper we use two methods, a second-order two-dimensional Monte Carlo analysis and probability bounds analysis, to investigate the impact of both types of uncertainty on the results of a food-web exposure model. We demonstrate how the full extent of uncertainty in a risk estimate can be fully portrayed in a way that is useful to risk managers. We show that probability bounds analysis is a useful tool for identifying the parameters that contribute the most to uncertainty in a risk estimate and how it can be used to complement established practices in risk assessment. We conclude by promoting the use of probability analysis in conjunction with Monte Carlo analyses as a method for checking how plausible Monte Carlo results are in the full context of uncertainty.     

Health risk assessment of arsenic in soils from three thermal power plants in Southwest China

Abstract

High levels of arsenic (As) contamination in soils from thermal power plants pose a great threat to human health. This study aimed to evaluate the As contamination levels and assess the possible health risk of As in soils from three typical thermal power plants in Southwest China. The concentration of As was detected by using novel collision/reaction cell technology (CCT) with inductively coupled plasma mass spectrometry (ICP-MS, collectively ICP-CCT-MS) after aseptic digestion of soil samples. The carcinogenic risk and hazard quotient were estimated for health risk to workers in the study area by using “Chinese Technical Guidelines for Risk Assessment of Contaminated Sites (HJ 25.3-2014)”. Results showed that the concentration of As was between 3.65 and 33.80?mg/kg, and the comprehensive carcinogenic risk level of As was 3–28 times over the maximum acceptable level (10^?6), indicating that workers in the study area are facing serious threat of As. Oral ingestion (76.65%) was the main exposure pathway to carcinogenic risk, followed by skin contact (13.15%) and inhalation of soil particles (10.20%). After calculating the safety threshold values under three different exposure pathways (oral ingestion, skin contact and inhalation of soil particles), the minimum safety threshold value (1.59?mg/kg) was selected as the reference safety threshold value of As in the study area. These results provide basic information of health risk assessment of As and environmental management in thermal power plant areas.     

Analysis of Worldwide Naphthalene Surface Soil Regulatory Guidance Values

Many environmental regulatory jurisdictions worldwide specify the maximum soil contamination mass burdens that may occur without prompting a regulatory response. For residential surface soils, these regulatory guidance values (RGVs) are generally based on human (often child) health risks from inhalation, ingestion, and dermal exposure to contamination. RGVs have been promulgated for more than 1,200 soil contaminants. Of these, naphthalene is the most frequently regulated contaminant. The 234 known naphthalene RGVs range from a minimum of 0.0289 mg/kg to a maximum of 16,000 mg/kg and span 5.7 orders of magnitude. Analysis illustrates that, although there are small non-random clusters of values, and there may be statistically significant differences between the values used in the U.S. and elsewhere around the world, the overall distribution of numbers strongly resembles (r = 0.9953) that of a log-normal random variable. Results of Monte Carlo uncertainty analysis applied to the U.S. Environmental Protection Agency risk model are presented to approximate the range of the naphthalene RGV span that can be attributed to uncertainty in cancer or non-cancer risk formulations. Uncertainty in the cancer risk formulation could account for approximately 41% of the RGVs. Uncertainty in the non-cancer risk formulation could account for a different 22% of the RGVs, but the cancer risk model generally yields the binding (lowest) value. The implications of these widely variable RGVs for health risk and remediation costs are discussed and methods of reducing variability are suggested.