Recent developments on the hazards posed by 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin in soil: Implications for setting risk‐based cleanup levels at residential and industrial sites

Abstract

Since the publication of the Times Beach risk assessment in 1984, which suggested that residential soils were of concern when the level of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was in excess of 1 ppb, there has been continued interest in this topic. Studies conducted within the past 5 yr on the environmental and toxicological behavior of TCDD, as well as refinement of parameters regarding human exposure, indicate that previous assessments of the risk to humans posed by TCDD-contaminated soil were overestimated. In this paper, recent information drawn from nearly 100 recently published articles regarding the histopathology interpretation of the Kociba bioassay, environmental fate and half-life of TCDD in soil, and estimates of human exposure via soil ingestion, dermal contact, inhalation, surface runoff, and the consumption of fish were incorporated into a risk assessment. Cleanup levels for TCDD in residential and industrial soils were calculated based on most likely exposure scenarios. Probability distributions of key exposure parameters were incorporated into a Monte Carlo uncertainty analysis to predict the range and probability of TCDD uptake and corresponding cleanup levels in soil. This analysis demonstrated that the most significant route of human exposure to TCDD is through dermal contact with soil, followed by soil ingestion, fish consumption, and inhalation of airborne particulates. At residential sites, soils containing 20 parts per billion (ppb) of TCDD were found to pose a lifetime cancer risk no greater than 1 in 100,000 (10(-5) risk) under typical exposure conditions. Based on the Monte Carlo analysis, soil concentrations for the 75th and 95th percentile person were 12 and 7 ppb (10(-5) risk), respectively. In industrial soils, TCDD concentrations ranged between 131 and 582 ppb (10(-5) risk), depending on the amount of time spent outdoors under typical exposure conditions. Industrial soil concentrations of approximately 93 and 46 ppb (10(-5) risk) were calculated for the 75th and 95th percentile worker, respectively, engaged in outdoor activities. The range of TCDD concentrations in industrial soils was not reduced significantly when the consumption of fish from a neighboring waterway by off-site receptors was considered. While cleanup levels for TCDD should be derived on a site-specific basis, this analysis indicated that soil cleanup standards can be generally higher than those implemented over the past 8 yr.

Biotransformation of Polychlorinated Dioxins and Microbial Community Dynamics in Sediment Microcosms at Different Contamination Levels

“…To our knowledge, this is the first report to clearly define the half-life of PCDD/Fs under a given set of conditions by studying kinetic information. The half-life of PCDD/Fs found in our microcosms is much shorter than that recorded in soil 44) and in lake sediment 38) . Consistent with results reported previously 60) , the present study showed that all PCDD/F congeners in the 4 microcosms were totally reduced without the accumulation of significant amounts of 1-3CDD/Fs as intermediate or end products.…”

Serum polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans among people eating contaminated home-produced eggs and beef.

“…Environmental and biologic half-lives, each of which may be measured in decades (33,35), strongly indicate that indirect dioxin exposure is a long-term problem. Future research should be directed at environmental fate and biologic uptake and elimination.…”

“…Eggs were also collected from chickens raised with access to soil at 23 additional homes in the greater Oroville area (21). We (35). Other potential industrial sources were located near the wood treatment facility; most notably, four teepee burners were within 2 km.…”

Distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in the landfill site for solidified monoliths of fly ash

“…Many studies indicate that the PCDD/Fs (particularly the more highly chlorinated congeners) possess such strong hydrophobicity and exhibit little downward mobility once deposited in or on soil [2][3][4][5][6]. Orazio et al [3] investigated the soil in the vicinity of a site contaminated by PCDD/Fs.…”