The Influence of Liquid to Soil Ratios on Arsenic and Lead Bioaccessibility in Reference and Field Soil

In vitro bioaccessibility testing is gaining popularity as a tool to estimate the oral bioavailability of contaminants in soil for human health risk assessment (HHRA). Bioaccessibility tests are used to measure the bioaccessible fraction of a contaminant in soil, which can then be used to estimate the bioavailable fraction. Inherent uncertainties are associated with bioaccessibility tests. Various test parameters need to be carefully considered in their development, including the liquid to soil (L/S) ratio employed. We used L/S ratios (v:wt) ranging from 25 ml:1 g to 1,000 ml:1 g in a modified relative bioaccessibility extraction procedure to investigate the effects on bioaccessibility of lead and arsenic in field and reference soils. General trends of increased percent bioaccessibility of lead and arsenic with increasing L/S ratio were observed in the reference soil. A similar positive relationship was observed for lead in the field soil; soluble arsenic concentrations were below the detection limit and data were insufficient to observe a trend. Percent bioaccessibility was significantly affected at each extreme of the L/S ratios tested (p < .05). Biological relevance, technical feasibility, and mathematical relationships with in vivo results should be considered when selecting an appropriate L/S ratio for bioaccessibility testing.     

Arsenic Pollution of a Loam Soil: Retention Form and Decontamination

A study was conducted to assess the retention form of arsenic in soil and to evaluate the use of phosphate for releasing it from the soil. In this study, a loam soil was artificially polluted with arsenate at pH 5.5, which is one of the pH values at which maximum arsenic adsorption occurred. The soil was kept for 2.5 months under wet conditions to allow for stabilization. The soil was maintained under aerobic condition and losses of arsenic by volatilization were determined to be minimal. The soil was then sequentially extracted with a series of chemicals to identify the soil fractions in which the arsenic was bound. The percentage of arsenic found in the Fe bound-exchangeable, reducible-residual, Al bound exchangeable, residual, calcium bound exchangeable, and easily exchangeable forms was 31.6, 27.3, 25.2, 5.5, 4.9, and 4.7%, respectively. A batch experiment showed that at 20°C, 80% of the bound arsenic was removed by phosphate in the pH range of 5 to 7. A power function model was found to fit the data with a desorption rate constant of 402?mg/kg As h^?1.     

Effects of Contaminant Concentration,Aging, and Soil Properties on the Bioaccessibility of Cr(III) and Cr(VI) in Soil

Contaminated soils at numerous U.S. Department of Defense, Department of Energy, and other industrial facilities often contain huge inventories of toxic metals such as chromium. Ingestion of soil by children is often the primary risk factor that drives the need for remediation. Site assessments are typically based solely on total soil-metal concentrations and do not consider the potential for decreased bioaccessibility due to metal sequestration by soil. The objectives of this research are to investigate the effect of soil properties on the bioaccessibility of Cr(III) and Cr(VI) as a function of contaminant concentration and aging. The A and upper B horizons of two well-characterized soils, representative of Cr-contaminated soils in the southeastern United States, were treated with varying concentration of Cr(III) and Cr(VI) and allowed to age. The bioaccessibility of the contaminated soils was measured over a 200-d time period using a physiologically based extraction test (PBET) that was designed to simulate the digestive process of the stomach. The sorption of Cr(III) and Cr(VI) varied significantly as a function of soil type and horizon, and the oxidation state of the contaminant. Solid phase concentrations with Cr(III) were significantly greater than Cr(VI) for any given initial Cr concentration. This is consistent with the mechanisms of Cr(III) vs. Cr(VI) sequestration by the soils, where the formation of Cr(III)-hydroxides can result in the accumulation of large mass fractions of contaminant on mineral surfaces. Overall, Cr bioaccessibility decreased with duration of exposure for all soils and at all solid phase concentrations, with aging effects being more pronounced for Cr(III). The decrease in Cr bioaccessibility was rapid for the first 50 d and then slowed dramatically between 50 and 200 d. In general, the effects of Cr solid phase concentration on bioaccessibility was small, with Cr(III) showing the most pronounced effect; higher solid phase concentrations resulted in a decrease in bioaccessibility. Chemical extraction methods and X-ray Adsorption Spectroscopy analyses suggested that the bioaccessibility of Cr(VI) was significantly influenced by reduction processes catalyzed by soil organic carbon. Soils with sufficient organic carbon had lower Cr bioaccessibility values (～10 to 20%) due to an enhanced reduction of Cr(VI) to Cr(III). In soils where organic carbon was limited and reduction processes were minimal, the bioaccessibility of Cr(VI) dramatically increased (～60 to 70%).     

Reducing the Leachability and Bioaccessibility of Arsenic in Soils using Supported Nano Titanium Dioxide

We herein report the development and testing of a novel material, namely activated carbon-supported nano titanium dioxide (ACTD) for the immobilization of arsenic in soil. This material, which was prepared using a sol-gel method, effectively reduced the toxicity characteristic leaching procedure (TCLP) leachability and physiologically based extraction test (PBET) bioaccessibility of As(III) in soil samples. Upon processing the soils for 56 d at an ACTD dosage of 0.25 mmol g^?1, the TCLP leachability of As(III) was reduced by 82.7–97.7%, while the bioaccessibility was lowered by 58.6–81.2%. In addition, sequential extraction resulted in an 11.5–96.0% decrease in the mobile-As(III) and the mobilizable-As(III) fractions, but an increase in the residual-As(III) fraction upon treatment with ACTD. These observations indicate that the application of ACTD could result in an 80% reduction in As(III) environmental leaching, thereby confirming that ACTD appears suitable for the treatment of arsenic-contaminated soil.     

Lead fractionation and bioaccessibility in contaminated soils with variable chemical properties

Abstract

The hazard imposed by trace elements within soils is dependent on soil properties and the relative distribution of metal species. Hence, a greenhouse column study was conducted to investigate the geochemical speciation and bioaccessibility of lead (Pb) as a function of soil properties. Four different soil types (Immokalee, Belle Glade, Tobosa and Millhopper series) varying in physico-chemical properties were selected and amended with Pb as Pb(NO₃) at 400, 800, and 1,200 mg kg^?1. A sequential extraction was employed to define the reactive metal pool, which was correlated with Pb bio-accessibility as determined by the physiologically based extraction test. Results show that Pb was mainly distributed in soluble+exchangeable phase in Immokallee (82%) and Millhopper (45%) series, and carbonate and Fe+Mn oxide fractions in Belle Glade (14–74%) and Tobosa (31–64%) series at time zero. With soil aging, Pb underwent chemical transformations in the soils and the majority of added Pb was associated with Fe+Mn oxide fraction (64–81%). Also, Pb bioaccessibility varied widely as a function of soil type and soil aging. Gastric phase (IVG-S) extracted 34–81% and 29–75% and the absorbed intestinal phase (IVG-AI) extracted 12–79% and 12–45% of amended Pb in all the soils at time zero and 6 months, respectively. Among soil types, Tobosa and Belle Glade showed reduced bioaccessibility relative to Immokalee and Millhopper. Statistical analysis revealed that the IVG-S Pb decreases as soil organic matter and cation exchange capacity (CEC) increases and total P decreases. While the Mehlich extractable P and Ca+Mg, total Fe+Al and organic matter predicted the Pb in an intestinal system.     

Treatment of Used Diesel Invert Drilling Mud to Remove Hydrocarbons,Fix Lead,and Leach Brine

A sample of used, highly saline diesel invert drilling mud (DIDM), artificially contaminated with lead, was tested for remediation using ICPET/ NRC's Solvent Extraction Soil Remediation (SESR) process. The work comprised investigation of the concurrent solvent extraction of diesel oil and fixation of lead by co-agglomeration of metal binding agents. Peat, soluble and insoluble phosphates, coal combustion fly ashes, and flue gas desulfurization scrubber sludge were tested as lead fixation agents. Virtually complete extraction of diesel oil was achieved in a five-step extraction process using toluene, trichloroethylene, or hexane as solvents. The effect of the metal fixation agents on solvent extraction efficiency was also investigated. After remediation to remove hydrocarbons and fix heavy metals, the DIDM sample remained saline. Successful leaching of brine from the dried agglomerates was accomplished by water percolation through a fixed bed of the dried, agglomerated soil. The cleaned DIDM was evaluated for resistance to acid leaching of lead using the U.S.-EPA's toxicity test method 1310A and Toxicity Characteristics Leaching Procedure method 1311. Long-term stability of the treated solids to acid leaching was tested using the U.S.EPA's multiple extraction procedure method 1320. Bioavailability of fixed lead to barley plants grown on synthetic soils prepared from remediated DIDM was determined by analyzing the roots and shoots for lead content. Acid phosphatase, peroxidase, and protein levels were determined in plant roots and soil leachates by biochemical analysis methods. These results were used to assess the effect of enzymes produced by plant root systems, or soil associated microorganisms, on the stability of fixed lead. The presence of fixation agents reduced the bioavailability of lead to the plants.     

Effects of Sterilization and Temperature on the Decrease Kinetic of Lead Bioavailability in Two Different Soil Groups

Sorption of metal ions by soil and clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The impacts of sterilization and incubation temperature on the decrease kinetic of Pb bioavailability in two different groups of soils were studied. Surface soils were sampled from Guilan and Hamadan provinces in the north and northwest of Iran with temperate and semiarid climates. The decrease kinetic of Pb bioavailability in the Pb(NO₃)₂ treated (400 μg Pb g^?1) soils has been studied in solid state incubation in sterile and unsterile conditions at 15, 27 and 37°C. The decrease of DTPA-extractable Pb in both groups of soils is often characterized by an initial rapid step followed by a slow step. The temperate soil with high affinity surface sites for Pb sorption compared to semiarid soils had a lower DTPA-extractable Pb in each time of extraction. Sterilization and soil incubation at lower temperature decreased the rate of Pb sorption/precipitation processes. Among the kinetic models the second order model and Elovich kinetic equation were the better choice to express the decrease kinetic of Pb bioavailability according to higher determined coefficient and the small standard error of the estimate. The determination coefficients of the mass transfer equation were increased and the standard errors of the estimates were decreased in sterile and unsterile conditions by increasing incubation temperature from 15 to 37°C.     

Lead Distribution and Mobility in a Soil Embankment Used as a Bullet Stop at a Shooting Range

The distribution of lead in and below a soil embankment used as a stop butt for lead bullets at a sport shooting range for more than 30 years was investigated. A vertical profile, just behind the shooting target, was mapped by 54 soil samples characterized by contents of lead bullets, soil lead, and easily leachable lead as measured in a leaching test (L/S 2). At the target, the soil contained up to 40% metallic lead and 5 to 10% lead associated with the soil particles (<2?mm). The leaching test showed concentrations of dissolved lead in the range 5 to 20?mg/l. However, in the bottom of the stop butt (about 1?m lower than the target) soil lead was only slightly elevated, and no increase in lead was found below the stop butt in the original soil profile. In the lower part of the stop butt, pH was around 5, which is considered to favor lead migration, but in the soil samples with lead bullets present pH was between 6 and 7. The elevated pH values, probably caused by the corrosion of lead bullets, may have been a significant factor in limiting the migration of lead in the stop butt. The investigation showed that the lead in the stop butt did not affect the surroundings, but that the high lead content of the soil would require that this be treated as waste if the facility was abandoned.     

Bioaccessibility of Mercury in Soils

The initial risk assessment for the East Fork Poplar Creek (EFPC) floodplain in Oak Ridge, Tennessee, a superfund site heavily contaminated with mercury, was based on a reference dose for mercuric chloride. Mercuric chloride, however, is a soluble mercury compound not expected to be present in the floodplain, which is frequently saturated with water. Previous investigations had suggested mercury in the EFPC floodplain was less soluble and therefore potentially less bioavailable than mercuric chloride, possibly making the results of the risk assessment unduly conservative. A bioaccessibility study, designed to measure the amount of mercury available for absorption in a child's digestive tract (the most critical risk pathway endpoint), was performed on 20 soils from the EFPC floodplain. The average bioac-cessible mercury for the 20 soils was 5.3%, compared with 100% of the mercuric chloride subjected to the same conditions. The alteration of the procedure to more closely mimic conditions in the digestive tract did not significantly change the results. Therefore, the use of a reference dose for mercuric chloride at EFPC, and potentially at other mercury-contaminated sites, without incorporating a corresponding bioavailability adjustment factor may overestimate the risk posed by the site.     

Transvenous Lead Extraction (TLE) Procedure: Experience from a Tertiary Care Center in Thailand

BackgroundTransvenous Lead Extraction (TLE) is a standard treatment for some late Cardiac Implantable Electronics Device (CIED) complications. The outcome of transvenous lead extraction procedure in Thailand is not robust.MethodsA Single-center retrospective cohort of TLE procedures performed at Ramathibodi hospital between January 2008 and December 2020 was studied.ResultsThere were 157 leads from 105 patients who underwent lead removal procedure during the specified period. Data analysis was performed from 79 TLE patients due to incomplete data and lead explant procedure of the excluded subjects. Mean patients’ age was 57.7 ± 18.7 years, with 70.9% male. There were 82 pacemaker leads, 35 ICD leads, and 5 CS leads (mean number of leads were 1.54 ± 0.66 per patient), with mean implanted duration of 87.8 ± 68.2 months. Main indication for TLE was infection-related, which accounted for 67.1% of the cases.Overall clinical success rate was 97.5%. Mean operative time was 163.8 ± 69.5 min. Major complications occurred in 4 patients (5.1%) with one in-hospital mortality from severe sepsis.ConclusionTLE using laser sheath and rotating mechanical sheath for transvenous lead extraction is effective and safe, even outside high-volume center.     

A Quick,Onsite Test for Delineating Arsenic Contaminant Plumes in Soil

Dipping vats were used routinely in the southeastern U.S. in the early 1900s to eradicate the cattle fever tick. The legacy is many dip vat sites with arsenic (As)-contaminated soil and ground water. Assessing the extent of these As plumes can be time consuming and expensive. We describe a quicker and less expensive, onsite test for soil As. It is a modification of a commercially available test designed for As in water, taking about 10?min to complete, allowing large plume areas to be delineated in a single day. An As contaminant plume in Alachua County, FL, was delineated using the quick test. Soil samples taken from a large grid encompassing the plume were analyzed in the laboratory for As to confirm the results obtained with the quick test. The comparison showed that the quick test very accurately delineated the outer boundary of the plume as well as zones of higher As concentration within the plume.     

Speciation and Vertical Distribution of Lead and Lead Shot in Soil at a Recreational Firing Range

In this study, the speciation, vertical distribution and soil particle size fractions of lead in soil samples at a recreational firing range was determined. This study was performed to gain a better understanding of how lead shot breaks down at ranges. Both the chemical form of lead and the types of soil particles with which lead is associated are important for understanding not only the mobility and persistence, but also the human and ecological impact of lead at these ranges. Lead as shot gun pellets was found to be the dominant form of lead in soil samples. The highest levels were measured in surface samples located in the “fall zone” of the range. Results indicate shot to be relatively absent below surficial samples. Lead concentrations in soil decreased markedly across a 0–6″ depth profile. Lead carbonates were the dominant non-shot form of lead present at all depths. Water-soluble lead species made up a minor fraction of the non-shot lead present in the samples. Based on soil particle sizes measured, highest concentrations of lead were measured in soil particles passing a 0.075 mm sieve.     

Removal of Lead from a Calcareous Soil by Chloride Complexation

Remediation of a lead-contaminated calcareous soil using NaCl solutions was examined. The removal of Pb from a coarser fraction of the soil was found to be 83% after three successive extractions at a NaCl concentration of 8?M, whereas an average of 9% of the calcium was removed. Multibatch extractions of Pb from finer soil containing a higher level of Pb were also performed. The removal of Pb from this soil after six successive extractions with 8?M NaCl was found to be 93%. The removal of Pb increased with time in a batch test and approached 80% after 90?h. It was found that the data were adequately described by a first-order rate, and hence it is believed that a single reaction mechanism controlled the release of Pb (i.e., from carbonate bound or exchangeable Pb fractions in the soil). Increasing removal of Pb was found as the volume of water added was increased as the mass of NaCl in solution remained constant. The removal of Pb from the leachate was found to be 90%, 99.7%, and 35% with lime (25.20?g/L), sodium carbonate (4.48?g/L), and calcium carbonate (82.0?g/L) addition, respectively. In the case of sodium carbonate, the removal of Pb was further improved when the pH was adjusted to 8.2. The recycling of free chloride that was generated from leachate resulted in 91% removal of Pb from the soil (particle size < 4.75?mm) after six recycles.     

Influence of Matrix Composition on the Bioaccessibility of Copper,Zinc, and Nickel in Urban Residential Dust and Soil

This study examines factors affecting oral bioaccessibility of metals in household dust, in particular metal speciation, organic carbon content, and particle size, with the goal of addressing risk assessment information requirements. Investigation of copper (Cu) and zinc (Zn) speciation in two size fractions of dust (< 36 μ m and 80–150 μ m) using synchrotron X-ray absorption spectroscopy (XAS) indicates that the two metals are bound to different components of the dust: Cu is predominately associated with the organic phase of the dust, while Zn is predominately associated with the mineral fraction. Total and bioaccessible Cu, nickel (Ni), and Zn were determined (on dry weight basis) in the < 150 μ m size fraction of a set of archived indoor dust samples (n = 63) and corresponding garden soil samples (n = 66) from the City of Ottawa, Canada. The median bioaccessible Cu content is 66 μ g g^?1 in dust compared to 5 μ g g^?1 in soil; the median bioaccessible Ni content is 16 μ g g^?1 in dust compared to 2 μ g g^?1 in soil; and the median bioaccessible Zn content is 410 μ g g^?1 in dust compared to 18 μ g g^?1 in soil. For the same data set, the median total Cu content is 152 μ g g^?1 in dust compared to 17 μ g g^?1 in soil; the median total Ni content is 41 μ g g^?1 in dust compared to 13 μ g g^?1 in soil; and the median total Zn content is 626 μ g g^?1 in dust compared to 84 μ g g^?1 in soil. Organic carbon is elevated in indoor dust (median 28%) compared to soil (median 5%), and is a key factor controlling metal partitioning and therefore bioaccessibility. The results show that house dust and soil have distinct geochemical signatures and should not be treated as identical media in exposure and risk assessments. Separate measurements of the indoor and outdoor environment are essential to improve the accuracy of residential risk assessments.     

Effects of Groundwater Irrigation and Petroleum Exploiting on Soil Arsenic Levels

In order to evaluate the combined effects of drip irrigation and petroleum extraction activities on As contamination and distribution in local soils, a total of 141 soil and 30 groundwater (GW) samples from field sites drip-irrigated with GW in Kuitun, Xinjiang, China were collected and analyzed arsenic (As) levels. Soil As levels ranged from 6.74 to 23.10 mg·kg^?1. For the field irrigated with As-loaded GW for 0.5-10 years, As levels in soils increased by 0.50-9.10 mg·kg^?1 as compared with the control soils. As levels in all top-layer (0-10 cm in thickness) irrigated soils A (0-5 cm away from dripper) were found to be higher than those in top-layer irrigated soils B (5-10 cm away from dripper). It was estimated that As in agricultural soils increased by approximately 11～3789 g·yr^?1·ha^?1 under drip irrigating, most of which in top-layer soils covering the plant roots. The widely used drip irrigation system in Kuitun enhanced the ecological and human-health threats of As via affecting its spread into soils. Furthermore, the petroleum exploiting activity further promoted As levels in local soils. Within a distance of 10～1000 m away from petroleum exploiting sites, the soil As level decreases significantly with the distance.     

Arsenic(V) biosorption by charred orange peel in aqueous environments

Biosorption efficiency of natural orange peel (NOP) and charred orange peel (COP) was examined for the immobilization of arsenate (As(V)) in aqueous environments using batch sorption experiments. Sorption experiments were carried out as a function of pH, time, initial As(V) concentration and biosorbent dose, using NOP and COP (pretreated with sulfuric acid). Arsenate sorption was found to be maximum at pH 6.5, with higher As(V) removal percentage (98%) by COP than NOP (68%) at 4 g L^?1 optimum biosorbent dose. Sorption isotherm data exhibited a higher As(V) sorption (60.9 mg g^?1) for COP than NOP (32.7 mg g^?1). Langmuir model provided the best fit to describe As(V) sorption. Fourier transform infrared spectroscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy analyses revealed that the –OH, –COOH, and –N-H surface functional groups were involved in As(V) biosorption and the meso- to micro-porous structure of COP sequestered significantly (2-times) higher As(V) than NOP, respectively. Arsenate desorption from COP was found to be lower (10%) than NOP (26%) up to the third regeneration cycle. The results highlight that this method has a great potential to produce unique ‘charred’ materials from the widely available biowastes, with enhanced As(V) sorption properties.     

An In Vitro Procedure for Estimation of Lead Relative Bioavailability: With Validation

The relative bioaccessibility leaching procedure (RBALP) is a simple, reproducible, and rapid in vitro procedure for estimating the in vivo (juvenile swine) relative bioavailability (RBA) of lead in solid media. Control of pH, temperature, and agitation are the most critical parameters of this in vitro procedure. The performance of the method was evaluated by triplicate analyses of each of 19 different test substances by the author and three independent laboratories, and comparison of the results to relative bioavailability (RBA) values measured in vivo. The results indicate that the RBALP measurements are strongly correlated with the in vivo RBA values (r² = 0.924, p < 0.0001), with an average absolute error of 10% and an average predictive error of 20%. Comparison of results within and between laboratories indicates that the procedure is highly reproducible, with inter-and intra-laboratory coefficients of variation of 4% and 6%, respectively, and within-sample precision of approximately 7%. Based on the results reported here, the RBALP can be effective in providing reliable estimates of lead RBA as predicted by the immature swine model. The method may also be valuable in evaluating site-specific differences in bioaccessibility, assessing remedial technologies intended to reduce lead RBA, providing a screening mechanism for futurein vivo studies, and providing insight into the chemical and physical factors that control lead bioavailability.     

Extraction of Arsenic and Heavy Metals from Contaminated Mine Tailings by Soil Washing

In this study, the soil washing technique has been used to treat mine tailings contaminated heavily with arsenic and heavy metals at Jingok mine, which is one of the abandoned mines in Korea. The results showed that phosphoric acid, citric acid, oxalic acid, and sodium metabisulfite were highly effective in extracting arsenic and heavy metals. Among them, oxalic acid was the most effective (especially for Pb, Cu, and Zn), as even a residual fraction of arsenic was partly extracted. The optimum concentration of washing reagent and the ratio between the mine tailings and washing reagent were found to be 0.5 M and 1:20, respectively. In addition, the extraction kinetics of arsenic and heavy metals was fast, in which the reaction time of 30 minutes was deemed to be a sufficient contact time. From the results, it may be concluded that the low pH of washing solution and the amount of dissolved Fe may be considered as the most important factors in the extraction of arsenic and heavy metals.     

Factors Controlling the Geochemical Partitioning of Trace Metals in Estuarine Sediments

The geochemical partitioning of trace metals in sediments is of great importance in risk assessment and remedial investigation. Selected factors that may control the partitioning behavior of Cu, Pb and Zn in non-sulfidic, estuarine sediments were examined with the use of combined sorption curve—sequential extraction analysis. This approach, which has not been previously used to examine estuarine sediments, allowed determination of sorption parameters for Cu, Pb and Zn partitioning to individual geochemical fractions. Partitioning behavior in sulfidic sediments was also determined by sequentially extracting Cu, Pb, and Zn from synthetic sulfide minerals and from natural sediment and pure quartz sand after spiking with acid-volatile sulfide (AVS). Trace metal sorption to the “carbonate” fraction (pH 5, NaOAc extraction) increased with metal loading due to saturation of sorption sites associated with the “Fe-oxide” (NH₂OH·HCl extraction) and “organic” (H₂O₂ extraction) fractions in non-sulfidic sediments. Freundlich parameters describing sorption to the “Fe-oxide” and “organic” fractions were controlled by the sediment Fe-oxide and organic carbon content, respectively. Sequential extraction of Cu from pure CuS, AVS-spiked sediment and AVS-spiked quartz sand showed that AVS-bound Cu was quantitatively recovered in association with the “organic” fraction. However, some AVS-bound Pb and Zn were recovered by the NH₂OH·HCl step (which has been previously interpreted as “Fe-oxide” bound metals) in the sequential extraction procedure used in this study. This indicates that the sequential extraction of Pb and Zn in sulfidic sediments may lead to AVS-bound metals being mistaken as Fe-oxide bound species. Caution should therefore be exercised when interpreting sequential extraction results for Pb and Zn in anoxic sediments.     

Bioaccessibility and other key parameters in assessing oral exposure to PAH-contaminated soils and dust: A critical review

Soil ingestion is an important pathway for human exposure to polycyclic aromatic hydrocarbon (PAH)-contaminated soils and dust for children (via ingesting hand residue) as well as for adults (via occupational exposure). An appropriate selection of exposure parameter values is essential for having an accurate risk assessment. This review addresses key parameters for estimating oral exposure to PAH-contaminated soils/dust, discusses their variability and uncertainty, and provides recommendations for value selection. Bioaccessibility (contaminant fraction solubilized in gastro-intestinal tract, available for entering bloodstream and reaching target organs) and soil ingestion rate are two key parameters for exposure assessment (usually characterized by large variability and/or uncertainty), followed by exposure frequency/duration and body weight.