Preliminary assessment of PCB risks to human and ecological health in the lower Passaic River

Concentrations of Aroclor mixtures and specific polychlorinated biphenyl (PCB) congeners were measured in surface sediments and aquatic biota (striped bass fillet, mummichog, and blue crab muscle and hepatopancreas) collected from the lower Passaic River. Several of the 47 surface sediment samples contained Aroclor concentrations that exceeded a National Oceanic and Atmospheric Administration (NOAA) benchmark level for "total PCBs" (22.7 micrograms/kg). Each of the 18 PCB congeners analyzed in aquatic biota was detected in one or more tissue samples, and numerous congeners were detected in every sample (IUPAC numbers 77, 105, 114, 118, 123, 126, 156, 157, 167, and 189). PCB congener concentrations were similar to those that have been reported in fish from other waterways that contain elevated levels of PCBs. Congener 118 was present at the highest concentration in almost all samples, and constituted 14-60% of the total PCB mass (sum of all congener masses) measured in any given tissue sample. In spite of the prevalence of PCB congeners in biota tissues (up to 1314 micrograms/kg total PCBs), Aroclors were not detected in bass or crab samples at a limit of detection of 33-55 micrograms/kg. This anomaly may be due to selective degradation of certain PCB congeners that are used to analytically recognize and quantitate Aroclors. Using the measured sediment concentrations, a food web model accurately predicted blue crab muscle concentrations of individual PCB congeners (typically within a factor of two) and was also fairly accurate for mummichog (typically within an order of magnitude). Concentrations in striped bass fillet were underestimated by factors of approximately 20-140. Increased cancer risk estimates associated with fish and crab consumption were obtained using four different methods. Using Aroclor tissue concentrations (one-half the limit of detection) and an Aroclor slope factor, total risks were 2.6 x 10(-6); using the "total PCB" measurements and an Aroclor slope factor, total risks were 1.9 x 10(-5); the "PCB-TEQ" method yielded total risks of 6.5 x 10(-4); and USEPA's recent suggested approach for evaluating "dioxin-like" and non-"dioxin-like" effects resulted in a total risk of 6.6 x 10(-4). This wide range in risk estimates indicates that it is critical to the risk management decision-making process that data requirements and risk assessment objectives be carefully evaluated early in the investigation process.

Current views on the oral bioavailability of inorganic mercury in soil: implications for health risk assessments

Due to the presence of mercury at a number of major contaminated sites in the United States, the bioavailability of inorganic mercury in soil following ingestion has emerged as an important public health issue. Studies of the leachability/solubility of inorganic mercury in soil have shown that it is largely immobile, thereby suggesting that it will not be readily available for absorption in the gastrointestinal tract. Ignoring the effect of the soil matrix on decreasing bioavailability may result in a substantial overprediction of risks due to ingestion of contaminated soil. This paper discusses current knowledge about the oral bioavailability of inorganic mercury in soil and offers suggestions about how these data may be applied in human health risk assessment. Though precise estimates are not available, in vivo and in vitro estimates of the bioavailability of different inorganic mercury species in different matrices suggest that the bioavailability of mercury in soil is likely to be significantly less, on the order of at least three- to tenfold, than the bioavailability of mercuric chloride, the species used to derive the toxicity criteria for inorganic mercury. Because bioavailability can vary significantly with soil type, soil aging, the presence of co-contaminants and other factors, it is suggested that whenever the fiscal aspects justify a more precise estimate of bioavailability, site-specific estimates be developed. To develop a database for identifying a less expensive and more efficient method for estimating bioavailability, it is suggested that in vivo studies be conducted concurrently with in vitro studies. However, due to the lack of precision associated with the derivation of the most widely-used health guidance value for inorganic mercury (the USEPA RfD), additional work to address the uncertainties in the RfD is recommended.

Urinary chromium as a biological marker of environmental exposure: what are the limitations?

Public concern has mounted recently about environmental exposures to chromium in soil, tap water, and ambient air. In response, agencies charged with protecting public health have attempted to study exposure by monitoring urinary chromium levels among potentially exposed populations. While urinary biomonitoring of occupationally exposed workers has been successfully used to assess high-level inhalation exposures in the workplace, evaluating low-level environmental exposures has been problematic. Due to these problems, before an extensive biological monitoring study is conducted of those exposed to low levels of environmental chromium, several issues must be resolved. First, exposures to chromium must occur at the same time as sampling, because the biological half-life of chromium in urine is very short (less than 2 days). Second, reduced bioavailability and bioaccessibility via the oral and dermal routes of exposure limit the capacity of urinary monitoring to measure environmental exposures (e.g., systemic dose is too small to be measured). Third, the dose of chromium must be sufficient such that it may be reliably measured above background levels in urine (range of 0.2 to 2 microg/liter) and above the analytical limit of detection (0.2 microg/liter). Fourth, the inter- and intrapersonal variability in background levels of urinary chromium is known to be significant and influenced by food and beverage intake, smoking, and exercise. Thus, the role of each factor must be carefully understood. Finally, it is imperative to have developed a complete understanding of the clinical significance of elevated urinary chromium levels before a study is performed, because higher than background levels, in and of themselves, are not indicative of a significant health concern. The route of exposure, valence of chromium to which people were exposed, exposure time, and duration must all be understood before the biological data can be implemented. We have conducted a total of nine human exposure studies over the past 3 years in an attempt to understand the kinetics of chromium and the impact on urinary, red blood cell (RBC), and plasma biomonitoring programs. The results of these studies are described here and our recommendations are offered for how to design and implement a urinary chromium biomonitoring study. In our view, given some evidence that the dose of hexavalent chromium [Cr(VI)] is sufficient to be measurable above background concentrations of total chromium [Cr(III) and Cr(VI)], duplicated measurements of chromium in plasma and RBCs are, in most cases, a more definitive gauge of environmental exposure than urinary biomonitoring.

Systemic uptake of chromium in human volunteers following dermal contact with hexavalent chromium (22 mg/L)

This study examined the systemic uptake of chromium in four human volunteers following three hours of contact with water containing hexavalent chromium [Cr(VI)] at a concentration of 22 mg/L. Volunteers were immersed below the shoulders in water at 91 +/- 2.5 degrees F. On the day prior to the experiment and for five days afterwards, samples of urine, plasma, and red blood cells (RBCs) were collected and analyzed for total chromium. Red blood cell chromium concentrations were used as a specific biomarker for systemic uptake of Cr(VI). Although total chromium concentrations in RBCs and plasma increased relative to historical background concentrations on the day of exposure, no sustained elevation of chromium concentrations was observed in RBCs or plasma of the volunteers tested. Since absorption of chromium in the hexavalent state would result in the irreversible binding of Cr(VI) to hemoglobin within the RBC (manifested as a sustained elevation of total chromium concentrations in the RBC), the pattern of blood uptake and urinary excretion observed was consistent with uptake and distribution of chromium in the trivalent state. Small increases were observed in the concentration of total chromium in urine within 48 h of exposure, indicating that some trivalent chromium [Cr(III)] may have penetrated the skin at a rate of about 3.3 x 10(-5) to 4.1 x 10(-4) micrograms/ cm2-h. In short, the data indicated that a 3-h contact with Cr(VI) at concentrations in water plausible for environmental exposure (e.g., swimming) was not expected to result in systemic uptake of measurable amounts of Cr(VI), although a small quantity of Cr(VI) may have penetrated the skin where it was subsequently reduced to Cr(III) prior to systemic uptake.

The relative susceptibility of animals and humans to the carcinogenic hazard posed by exposure to 2,3,7,8-TCDD: an analysis using standard and internal measures of dose

An analysis of the carcinogenic dose-response for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in humans and animals was performed based on measured tissue and serum concentrations and using alternatives to administered dose as the dosimetric. The TCDD-related carcinogenic response in rats (female rat liver tumors from Kociba et al., using revised pathology from Goodman and Sauer, was compared to that in humans (lung cancer rates in Fingerhut et al.,). Three dosimetries were used: serum lipid TCDD area-under-the-curve (AUC), peak serum lipid concentration (Cpeak) and average serum lipid concentration (Cavg). Rat serum concentration-time profiles were estimated based on measured adipose lipid TCDD concentrations at the end of the Kociba et al. bioassay, assuming first-order elimination and a half-life of 25 days. Human concentration-time profiles were estimated based on measured serum lipid TCDD concentrations and known dates of first and last exposure, with an assumed 7.5 year half-life and first-order elimination. Comparison of rat and human responses indicated that, using all three of these dosimetries, humans are much less sensitive than rats to the carcinogenic effects of TCDD. Regardless of the dosimetric chosen, the cancer mortality in humans in the NIOSH cohort, if due to TCDD, is relatively insensitive to dose as defined in Fingerhut et al., [3]. Our analysis indicates that human exposure to background levels of TCDD (about 5 ppt serum lipid concentration) is not likely to produce an incremental cancer risk.

Ingestion of chromium(VI) in drinking water by human volunteers: absorption, distribution, and excretion of single and repeated doses

This study examines the magnitude of hexavalent chromium [Cr(VI)] absorption, distribution, and excretion following oral exposure to 5 and 10 mg Cr(VI)/L in drinking water administered as a single bolus dose (0.5 L swallowed in 2 min) or for 3 d at a dosage of 1 L/d (3 doses of 0.33 L each day, at 6-h intervals). Adult male volunteers ingested deionized water containing various concentrations of potassium chromate, and samples of urine, plasma, and red blood cells (RBCs) were collected and analyzed for total chromium throughout the studies. In the bolus dose studies, a fairly consistent pattern of urinary chromium excretion was observed, with an average half life of about 39 h. However, 4-d total urinary chromium excretion and peak concentrations in urine and blood varied considerably among the 5 volunteers. Studies of repeated exposure to smaller volumes ingested at a more gradual rate (i.e., 0.33 L over 5-15 min) showed similar urinary chromium excretion patterns but generally lower chromium uptake/excretion. Given that sustained elevations in RBC chromium levels provide a specific indication of chromium absorption in the hexavalent state, these data suggest that virtually all (> 99.7%) of the ingested Cr(VI) at 5 and 10 mg Cr(VI)/L was reduced to Cr(III) before entering the blood-stream. The interindividual differences in total chromium uptake and excretion are plausibly explained by ingestion of appreciable doses on an empty stomach, which likely results in the formation of well-absorbed Cr(III) organic complexes in gastrointestinal tissues and possibly the blood. The lack of any clinical indications of toxicity in the volunteers and the patterns of blood uptake and urinary excretion of chromium are consistent with a predominant uptake of Cr(III) organic complexes [derived from Cr(VI)] that are excreted more slowly than inorganic forms of Cr(III). Therefore, it appears that the endogenous reducing agents within the upper gastrointestinal tract and the blood provide sufficient reducing potential to prevent any substantial systemic uptake of Cr(VI) following drinking-water exposures at 5-10 mg Cr(VI)/L. Based on these data, the chemical environment in the gastrointestinal tract and the blood is effective even under relative fasting conditions in reducing Cr(VI) to one or more forms of Cr(III).

Human ingestion of chromium (VI) in drinking water: pharmacokinetics following repeated exposure

Regulatory agencies have established safe drinking water concentrations for hexavalent chromium [Cr(VI)] based in part on the presumed capability of human gastric juices to rapidly reduce Cr(VI) to nontoxic trivalent chromium [Cr(III)] prior to systemic absorption. This study examines dose-related pharmacokinetics in humans following repeated oral exposure to Cr(VI) in drinking water. In particular, we sought to examine whether plausible drinking water exposures to Cr(VI) caused a sustained increase in red blood cell chromium levels, a specific marker for systemic uptake of Cr(VI). Adult male volunteers ingested a liter (in three volumes of 333 ml, at approximate 6-hr intervals) of deionized water containing Cr(VI) concentrations ranging from 0.1 to 10.0 mg/liter. Samples of urine, plasma, and red blood cells were collected and analyzed for chromium. A dose-related increase in urinary chromium excretion was observed in all volunteers. Red blood cell and plasma chromium concentrations became elevated in certain individuals at the highest doses. The RBC chromium profiles suggest that the ingested Cr(VI) was reduced to Cr(III) before entering the bloodstream, since the chromium concentration in the RBCs dropped rapidly postexposure. These findings suggest that the human gastrointestinal tract has the capacity to reduce ingested Cr(VI) following ingestion of up to 1 liter of water containing 10.0 mg/liter of Cr(VI), which is consistent with USEPA's position that the Cr(VI) drinking water standard of 0.10 mg Cr(VI)/liter is below the reductive capacity of the stomach.

Observation of steady state in blood and urine following human ingestion of hexavalent chromium in drinking water

The uptake and elimination of Cr(VI) in a male volunteer who ingested 2 L/d of water containing 2 mg/L for 17 consecutive days was measured. Total chromium was measured in urine, plasma, and red blood cells (RBCs) for 4 d prior to and 2 wk after dosing (34 d total). The estimated bioavailability (2%) and the plasma elimination half-life (36 h) were consistent with our previous studies of Cr(VI) ingestion in humans. Steady-state chromium concentrations in urine and blood were achieved after 7 d of Cr(VI) ingestion. Both plasma and red blood cell (RBC) chromium concentrations returned rapidly to background levels within a few days after cessation of dosing. Since the concentration of chromium in the RBC should not decrease quickly if the chromium had entered the RBC as Cr(VI), these data support our prior work suggesting that concentrations of 10 mg Cr(VI)/L or less in drinking water of exposed humans appears to be completely reduced to Cr(III) prior to systemic distribution. Clinical chemistry data indicate that no toxicity occurred.

Absorption and elimination of trivalent and hexavalent chromium in humans following ingestion of a bolus dose in drinking water

These studies investigate the magnitude and valence state of chromium absorbed following plausible drinking water exposures to chromium(VI). Four adult male volunteers ingested a single dose of 5 mg Cr (in 0.5 liters deionized water) in three choromium mixtures: (1) Cr(III) chloride (CrCl3), (2) potassium dichromate reduced with orange juice (cr(III)-OJ); and (3) potassium dichromate [Cr(VI)]. Blood and urine chromium levels were followed for 1-3 days prior to and up to 12 days after ingestion. The three mixtures showed quite different pharmacokinetic patterns. CrCl3 was poorly absorbed (estimated 0.13% bioavailability) and rapidly eliminated in urine (excretion half-life, approximately 10 hr), whereas Cr(III)-OJ was absorbed more efficiently (0.60% bioavailability) but more slowly (half-life, approximately 17 hr), and Cr(VI) had the highest bioavailability (6.9%) and the longest half-life (approximately 39 hr). All three chromium mixtures caused temporary elevations in red blood cell (RBC) and plasma chromium concentrations, but the magnitude and duration of elevation showed a clear trend (Cr(VI) > Cr(III)-OJ > CrCl3). The data suggest that nearly all the ingested Cr(VI) was reduced to Cr(III) before entering the bloodstream based on comparison to RBC and plasma chromium patterns in animals exposed to high doses of Cr(VI). These findings support our prior work which suggests that water-soluble organic complexes of Cr(III) formed during the reduction of Cr(VI) in vivo explain the patterns of blood uptake and urinary excretion in humans at drinking water concentrations of 10 mg/liter or less.

Measurement of DNA-protein cross-links in human leukocytes following acute ingestion of chromium in drinking water

Increased DNA-protein cross-linking (DPX) in circulating leukocytes has been proposed as a potential biomarker for exposure and genotoxic damage caused by inhalation of certain reactive chemicals, such as hexavalent chromium [Cr(VI)]. This study was designed to determine whether ingestion of a single dose of potassium dichromate alone [Cr(VI)] or potassium dichromate fully reduced to Cr(III) with orange juice (prior to ingestion) causes an increase in DPX of circulating leukocytes in humans. Four adult male volunteers ingested a bolus dose of 5000 micro chromium in a 0.51 volume of water (10 p.p.m.), and blood samples were collected at 0, 60, 120, 180 and 240 min afterwards for analysis of DPX formation in circulating leukocytes. Results were compared to each person's own background concentration of DPX in leukocytes. Blood and urine samples were also collected for up to 2 weeks following the dose to examine the pattern of uptake and excretion of chromium. The results showed that there was no significant change in DPX observed following either Cr(VI) or Cr(III) ingestion, even though blood and urine chromium measurements indicated systemic uptake of a substantial fraction of the ingested chromium. Since Cr(III) does not possess DPX-inducing properties while Cr(VI) does, these results suggest that the Cr(VI) was reduced to Cr(III) intragastrically prior to absorption or that the amount of Cr(VI) absorbed into the blood was insufficient to produce DPX. These results are consistent with prior research that indicated that DPX would not occur following exposure to Cr(VI) except at very high doses.

Urinary chromium concentrations in humans following ingestion of safe doses of hexavalent and trivalent chromium: implications for biomonitoring

In this study, we evaluate the significance of increased urinary chromium concentrations as a marker of chromium exposure and potential health risk. Six human volunteers ingested trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] at doses that are known to be safe but are much higher than typical dietary levels. The following dosing regimen was used: d 1-7, 200 micrograms/d chromium picolinate (a dietary supplement); d 8-10, Cr(VI) ingestion at the U.S. Environmental Protection Agency (EPA) reference dose (RfD) of 0.005 mg/kg/d; d 11-13, no dose; d 14-16, Cr(III) ingestion at the U.S. EPA RfD of 1.0 mg/ kg/d; and d 17-18, postdose. Urine voids were collected throughout the dosing periods and analyzed for chromium. Our findings are as follows: (1) ingestion of 200 micrograms/d of chromium picolinate yielded significantly elevated urine concentrations such that each participant routinely exceeded background, (2) ingestion of the Cr(VI) RfD (0.005 mg/kg/d) yielded individual mean urinary chromium levels (1.2-23 micrograms/L) and a pooled mean urinary chromium level (2.4 micrograms/L) that significantly exceeded background, and (3) ingestion of the Cr(III) RfD yielded no significant increase in urinary chromium concentrations, indicating that little, if any, absorption occurred. Our work identified three critical issues that need to be accounted for in any future studies that will use urinary chromium as a marker of exposure. First, a minimum urinary chromium concentration of approximately 2 micrograms/L should be used as a screening level to critically identify individuals who may have experienced elevated exposures to chromium. Second, if Cr(III) levels in soils are known to be less than 80,000 ppm and the Cr(III) is insoluble, urinary chromium concentrations are not an appropriate marker of exposure. Third, newer forms of chromium supplements that contain organic forms of Cr(III) must be considered potential confounders and their contribution to residential chromium uptake must be carefully evaluated.

Assessment of airborne hexavalent chromium in the home following use of contaminated tapwater

Field studies were conducted to estimate the plausible uptake of hexavalent chromium [Cr(VI)] aerosols inhaled during indoor residential use of a shower or an evaporative cooler supplied with water containing Cr(VI). In the evaporative cooler study, water concentrations of 20 mg Cr(VI)/L did not produce an increased concentration of airborne Cr(VI). The indoor air concentration of Cr(VI), measured over 24 hours of use, was 0.3-2.7 ng/m3, about the same as the concurrent outdoor concentrations. In the shower study, the average airborne concentrations of Cr(VI) aerosols at breathing-zone height ranged from 87 to 324 ng Cr(VI)/m3 when the water concentration of Cr(VI) was 0.89 to 11.5 mg/L. The Cr(VI) concentration in air was correlated directly to water concentration. The lifetime average daily doses and incremental cancer risk estimates corresponding to 30-year residential exposures were calculated using the measurements in this study and published exposure guidelines. The plausible upperbound lifetime cancer risk associated with continuous exposure to "background" Cr(VI) in outdoor air was estimated at 6.9 per million for a person exposed during ages 0-30, and 4.0 per million for ages 30-60. Similarly estimated upperbound cancer risks due to inhalation of shower aerosols from water containing 2-10 mg Cr(VI)/L over the same exposure period ranged from 0.9 to 5.5 per million. Our calculations demonstrate that shower aerosols do not contribute appreciably to background Cr(VI) exposures and risks, even at concentrations exceeding 2 mg Cr(VI)/L, which exhibit a discernible and unaesthetic yellow color that may limit the potential for long-term exposures of this type. We conclude that exposure to indoor aerosols from water containing Cr(VI) is unlikely to create a health hazard at concentrations up to 10 mg Cr(VI)/L. Furthermore, these aerosol measurements may be relevant to estimating airborne exposures to other nonvolatile chemicals.

Refined exposure assessment for ingestion of tapwater contaminated with hexavalent chromium: consideration of exogenous and endogenous reducing agents

Laboratory studies were conducted to determine how rapidly and completely chromium (VI) [Cr(VI)] is reduced upon contact with common beverages mixed with tapwater. Studies were performed for five common beverages (coffee, tea, orange juice, Kool Aid, and powdered lemonade) spiked with either 10 or 50 mg Cr(VI)/l. The concentrations of Cr(VI) were measured at several time intervals for up to four hours. It was demonstrated that each of these beverages had the capacity to reduce a concentration of > or = 8 mg Cr(VI)/l within a 15-minute time frame, and that continued monitoring of the beverages revealed greater reduction of the Cr(VI). These findings are consistent with the observation that many foods and beverages, as well as endogenous body fluids such as saliva and gastric juices, are capable of reducing substantial quantities of Cr(VI) to Cr(III). Our exposure assessment shows that the estimated high-end ingested dose of Cr(VI) from tapwater at both 1 and 5 mg Cr(VI)/l is generally two to three orders of magnitude below doses shown to have no adverse health effect in animal studies. When considered in conjunction with studies demonstrating that the reductive capacity of gastric juices may exceed 50 mg Cr(VI) daily, these observations suggest that little or no Cr(VI) is likely to be absorbed orally at a reasonable water concentration of Cr(VI), since tapwater is bright yellow at 5 mg Cr(VI)/l.

Biological relevance and consequences of chemical- or metal-induced DNA cross-linking

A vast number of chemicals are known to induce mutagenesis and/or carcinogenesis in mammals. Although disruption of cellular nuclear material resulting ultimately in mutagenesis/carcinogenesis can be accomplished by various mechanisms, the search for biomarkers of chemical-induced toxicity continues. This review focuses on the ability of certain metals or chemicals to bind to DNA in a cross-link fashion in whole animal as well as under in vitro conditions. The methodologies currently used to determine DNA cross-linking are described. The biological relevance of the presence of chemical- or metal-induced DNA cross-linking as a measure of carcinogenesis in humans is still under debate, as there is no clear correlation between the disease and the DNA cross-link reaction.

Physiologically based pharmacokinetic and pharmacodynamic modeling in health risk assessment and characterization of hazardous substances

Recent advances in physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) modeling have introduced novel approaches for evaluating toxicological problems. Because PBPK models are amenable to extrapolation of tissue dosimetry, they are increasingly being applied to chemical risk assessment. A comprehensive listing of PBPK/PD models for environmental chemicals developed to date is referenced. Salient applications of PBPK/PD modeling to health risk assessments and characterization of hazardous substances are illustrated with examples.

Urinary excretion of chromium following ingestion of chromite-ore processing residues in humans: implications for biomonitoring

Biomonitoring programs for urinary chromium (Cr) typically attempt to evaluate occupational exposure via the inhalation route. This study investigated whether Cr can be detected in the urine of people following the ingestion of soils that contain relatively high concentrations of chromium in chromite ore processing residue (COPR). To evaluate the reasonableness of using urinary monitoring to assess environmental exposure, six volunteers ingested 400 mg of soil/day (low-dose group), two others ingested 2.0 g of soil/day (high-dose group) for 3 consecutive days, and one person ingested a placebo on each of 3 days. The soil and COPR mixture contained concentrations of total chromium (Cr) and hexavalent chromium [Cr(VI)] of 103 +/- 20 and 9.3 +/- 3.8 mg/kg, respectively. Therefore, the low-dose group ingested 41 micrograms Cr/day [including 3.7 micrograms Cr(VI)] and the high-dose group ingested 206 micrograms Cr/day [including 18.6 micrograms Cr(VI)] on each of 3 consecutive days. All urine samples were collected and analyzed individually for total Cr on the day prior to dosing, during the 3 days of dosing, and up to the first void 48 h after the last dose. No significant increases in urinary Cr excretion were found when background excretion data were compared with data following each of the 3 days of dosing or in daily mean urine concentrations of the high- vs the low-dose groups. It appears that Cr present in a soil and COPR mixture at Cr doses up to 200 micrograms/day is not sufficiently bioavailable for biomonitoring of urine to be informative.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of probabilistic methods to understand the conservatism in California's approach to assessing health risks posed by air contaminants

Many state and federal agencies have prepared risk assessment guidelines, which describe methods for quantifying health risks associated with exposure to vapors and particulates emitted from point and area sources (e.g., California Air Pollution Control Officers Association [CAPCOA] under the Air Toxics "Hot Spots" Act [Assembly Bill 2588] and the U.S. Environmental Protection Agency [EPA] under the Clean Air Act). In general, these guidelines recommend or require the use of upperbound "point" estimates for numerous exposure parameters. This methodology yields a single risk estimate, which is intended not to underestimate the true risk and may significantly overstate it. This paper describes a risk assessment of a facility's airborne emissions using a probabilistic approach, which presents a range and distribution of risk estimates rather than a single point estimate. The health risks to residents living near a food processing facility, as estimated using techniques recommended by California AB2588, are compared to the results of a probabilistic analysis. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were identified as the emitted chemicals of concern. The point estimate method recommended by CAPCOA resulted in estimates that were greater than the 99.99th percentile risk predicted by the probabilistic analysis. As shown in other assessments of persistent airborne chemicals, secondary or indirect exposure pathways (i.e., ingestion of beef, ingestion of cow's milk, and ingestion of mother's milk) rather than inhalation, were the greatest contributors to risk. In this analysis, the probability distributions for the cancer potency factor and ingestion of cow's milk had the largest impact on the results of the 33 exposure factors considered.

Urinary excretion of chromium by humans following ingestion of chromium picolinate. Implications for biomonitoring

This study investigated the variability in urinary chromium (Cr) excretion following the ingestion of Cr picolinate by human volunteers. A pharmacokinetic model was used to estimate the bioavailability of Cr from ingested Cr picolinate using known distribution patterns and elimination rates of Cr by humans. The possible advantages of using sequential, individual spot, or 24-hr urine sample collection for biomonitoring of Cr exposure were examined. Background concentrations of urinary Cr determined from the spot samples in this study compared well with values reported by others. The variability in urinary excretion of Cr in untreated volunteers indicated that it is virtually impossible to distinguish exposures to most occupational and virtually all environmental exposures to Cr. Sequential urine sampling was found superior to both 24-hr and spot urine collection for indicating exposure to Cr picolinate. The extent of absorption of Cr from the picolinate matrix in the gastrointestinal tract was 2.80 +/- 1.14% (SD). It was estimated that 10 mg of soil containing between 7,400 and 52,000 mg Cr(III)/kg would have to be ingested by an adult to result in urinary excretion of Cr clearly above the upper bound of Cr in urine from background populations (1.8 microgram Cr/liter), depending on certain assumptions regarding bioavailability. This study supports the results of other recent work that demonstrated urinary excretion of Cr resulting from low-level environmental exposure is unlikely to be distinguished from that resulting from dietary uptake.

PCB and dioxin re-entry criteria for building surfaces and air

A number of fires involving polychlorinated biphenyl (PCB)-containing transformers and capacitors have occurred in the United States. PCB fires generate by-products such as polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs) and, when the transformer is in a building, contaminate the interior. Considerable concern exists over the potential human health effects associated with exposure by inhabitants to residual levels of PCBs, PCDFs and PCDDs. Office workers, for example, may be exposed to these chlorinated compounds via inhalation of contaminated particulates and vapors, dermal contact with contaminated surfaces, and incidental ingestion of dusts. A wide range of re-entry or cleanup levels have been developed for PCDDs and PCBs to protect workers who re-occupy a building following a PCB fire. Re-entry criteria have been used by property owners and regulatory agencies to determine whether the building is safe to re-occupy or to determine the extent of needed remediation. This paper presents a mass balance approach to deriving risk-based re-entry surface and air criteria for PCBs and PCDD/PCDFs. These criteria were based on a lifetime risk level of 10(-5), recent toxicological data on PCDDs and PCBs, and plausible exposure scenarios. Our analysis suggests that 125 ng/m2 2,3,7,8-TCDD TEQ for surfaces and 10 pg/m3 for air are acceptable. Based on Aroclor 1260, risk-based re-entry criteria for PCBs on surfaces and in air were 750 micrograms/m2 and 0.1 microgram/m3, respectively. In comparison to most previous guidelines, these risk-based criteria are less stringent, but can still be considered conservative. The surface criteria are 5 to up to 125 fold higher than previous guidelines. Air criteria range up to 5 times higher than criteria used at past PCB fire sites. Air concentrations associated with these were modeled and were negligible. For PCBs in air, the NIOSH guideline of 1 microgram/m3 is also appropriate for occupational settings.

Benzene toxicity and risk assessment, 1972-1992: implications for future regulation

Acute and chronic exposure to benzene vapors poses a number of health hazards to humans. To evaluate the probability that a specific degree of exposure will produce an adverse effect, risk assessment methods must be used. This paper reviews much of the published information and evaluates the various risk assessments for benzene that have been conducted over the past 20 years. There is sufficient evidence that chronic exposure to relatively high concentrations of benzene can produce an increased incidence of acute myelogenous leukemia (AML). Some studies have indicated that benzene may cause other leukemias, but due to the inconsistency of results, the evidence is not conclusive. To predict the leukemogenic risk for humans exposed to much lower doses of benzene than those observed in most epidemiology studies, a model must be used. Although several models could yield plausible results, to date most risk assessments have used the linear-quadratic or conditional logistic models. These appear to be the most appropriate ones for providing the cancer risk for airborne concentrations of 1 ppb to 10 ppm, the range most often observed in the community and workplace. Of the seven major epidemiology studies that have been conducted, there is a consensus that the Pliofilm cohort (rubber workers) is the best one for estimating the cancer potency because it is the only one with good exposure and incidence of disease data. The current EPA, OSHA, and ACGIH cancer potency estimates for benzene are based largely on this cohort. A retrospective exposure assessment and an analysis of the incidence of disease in these workers were completed in 1991. All of these issues are discussed and the implications evaluated in this paper. The range of benzene exposures to which Americans are commonly exposed and the current regulatory criteria are also presented.

Designing a biological monitoring program to assess community exposure to chromium: conclusions of an expert panel

The possible benefits of biological monitoring of large groups of people potentially exposed to environmental contaminants has become an area of much interest in recent years. Because chromite-ore processing residue has been found in some soils in northern New Jersey, urinary chromium monitoring of people in the community was evaluated as a potentially useful tool. In an attempt to identify those who could be exposed and to quantify the magnitude of exposure to the chromium in these soils, the New Jersey Department of Health (NJDOH) initiated a public health screening project. In 1992, the NJDOH proposed to evaluate over 4000 people who lived or worked near these sites. Volunteers were administered a questionnaire and were given a limited physical examination, and a single spot urine sample was collected. Because of the difficulties in using urinary chromium to assess low-level exposure and the potential implications of any regulatory decisions that could be based on the results of this project, a panel of experts was convened to evaluate the protocol. The panel consisted of five scientists and physicians with expertise in toxicology, dermatology, epidemiology, biological monitoring, and analytical chemistry. Like a World Health Organization group, the panel concluded that although urine biomonitoring can be useful in evaluating high levels of exposure to chromium, it is not reliable for assessing low-level exposure similar to that which may have occurred in northern New Jersey. The panel also noted that when urinary biomonitoring is to be used to assess the public's possible exposure, a large number of precautions must be taken to ensure the accuracy and usefulness of the results. The single most important recommendation was to collect a second, and perhaps a third, spot urine (or 24-h urine) sample before concluding that a person may be routinely overexposed. These suggestions are applicable to designing a biomonitoring program for nearly any environmental contaminant to which a community may be exposed. A review of scientific literature associated with biological monitoring of chromium is provided.

Evaluating the adequacy of maximum contaminant levels as health-protective cleanup goals: an analysis based on Monte Carlo techniques

At many sites in the United States, health-based remediation goals for contaminated groundwater have been set at levels far below USEPA's drinking water standards (i.e., maximum contaminant levels or MCLs). This is due to the fact that, while the USEPA must often consider technical and economic factors (e.g., cost of compliance, risk/benefit analysis) when setting MCLs for public water systems, cleanup goals for contaminated groundwater are often based solely on conservative "point" estimates of exposure. One of the more recent refinements in the risk assessment process is the use of ranges of exposure estimates or "probability density functions" (PDFs), rather than fixed point estimates, to estimate exposure and chemical uptake. This approach provides a more thorough description of the range of potential risks, rather than a single "worst-case" value, and allows one to understand the conservatism inherent in assessments based on regulatory default parameters. This paper uses a number of PDFs and the Monte Carlo technique to assess whether the USEPA's MCLs for drinking water are sufficiently low to protect persons exposed to these levels. A case study involving daily exposure to tapwater containing MCL concentrations of tetrachloroethylene, chloroform, bromoform, and vinyl chloride is presented. Several direct and indirect exposure pathways are evaluated, including inhalation and dermal contact while showering, direct ingestion, and inhalation of emissions from household fixtures and appliances. PDFs for each exposure factor are based on the most recent and applicable data available. Our analysis indicates that the estimated increased cancer risks at the 50th and 95th percentile of exposure are within the range of increased cancer risks typically considered acceptable at Superfund sites (10(-4)-10(-6)). These results suggest that, at least for some chemicals, groundwater need not be cleaned-up to concentrations less than drinking water standards (i.e., MCLs) to protect human health.