A model to predict threshold concentrations for toxic effects of chlorinated benzenes in sediment

Abstract

Abstract-A probabilistic model was developed to predict effects threshold concentrations for chlorinated benzenes in sediment. Based on published quantitative structure-activity relationships relating the toxicity of chlorinated benzenes to the degree of chlorination, congeners with the same number of chlorine substitutions were considered toxicologically equivalent. Hexachlorobenzene was excluded from the assessment based on a lack of aquatic toxicity at the water solubility limit. The equilibrium partitioning approach was applied in a probabilistic analysis to derive predicted effects thresholds (PETs) for each chlorinated benzene group, with model input distributions defined by published log K ow values and aquatic toxicity data (LC50s and acute to chronic ratios) extracted from the published literature. The probabilistic distributions of PETs generally increased with chlorination, with 20th percentile values ranging from 3.2 mg/kg 1%OC for chlorobenzene to 67 mg/kg 1%OC for tetrachlorobenzene congeners. The toxicity of total chlorinated benzenes in sediment can be assessed by applying the PETs in a toxic index model, based on the assumption that multiple chlorinated benzene congeners will show approximately additive toxicity, as characteristic of nonpolar narcotic toxicants. The 20th percentile PET values are one to two orders of magnitude higher than published screening-level guidelines, suggesting that the screening-level guidelines will provide overly conservative assessments in most cases. Relevant spiked sediment toxicity data are very limited but seem consistent with the probabilistic model; additional testing could be conducted to confirm the model's predictions.

Three lines of evidence in a sediment toxicity evaluation for hexachlorobutadiene

“…However, no chemicals other than HCBD were identified as potentially significant contributors to toxicity in any sample containing less than 3 mg/kg 1%OC HCBD. Specifically, hexchlorobenzene concentrations in all samples were well below the no‐effect concentrations observed in spiked sediment toxicity tests [9,34], toxic index values for other chlorinated benzenes [12] were well below levels expected to produce toxicity, and toxic index values for PAHs [11] were below the level associated with a 25% probability of toxicity. Additionally, Sferra et al [35] examined mercury concentrations in the dilution study as well as subsequent site‐specific tests and concluded that mercury‐related toxicity was not evident.…”

“…Methods used in the probabilistic comparison between the results of this study and those of published aquatic toxicity studies are described by Fuchsman et al [12]. The comparison is based on the equilibrium partitioning approach [10], which is typically expressed as where f oc = fraction organic carbon, and K oc = organic carbon/water partition coefficient.…”

“…Specifically, input values were randomly selected from the defined input distributions 10,000 times to calculate a distribution of predicted effects thresholds. The sensitivity of the predicted effects threshold distribution to variation in the input distributions was calculated during the Monte Carlo simulation as described by Fuchs‐man et al [12].…”

The reorganized brain: How treatment strategies for stroke and amblyopia can inform our knowledge of plasticity throughout the lifespan

“…This species differences in the magnitude of the response may be influenced by both biological variables (sex, age, spawning status, size, and genetic strain) and habitat variables (temperature, pH, and water flow) (Stegeman and Chevion, 1980; Koivusaari et al, 1981; Luxon et al, 1987; Lindström‐Seppä, 1985; Pedersen et al, 1976; Jimenez and Burtis, 1989). Additionally, large species differences in the induction measured during field studies may be due to variations in exposure, accumulation or sensitivity to inducers (Fuchsman et al, 1999). In this study none of the investigated fish species where exclusive carnivores or herbivores, their calculated trophic level ranged from 2.0 ± 0.00 (nose carp) to 3.03 ± 0.46 (chub) (Froese and Pauly, 2000).…”

Optimizing interpretation of in situ effects of riverine pollutants: Impact of upwelling and downwelling

“…The measured levels of CBs in many pore‐water samples from minipiezometers either approached or were above published aqueous concentrations that cause toxicity in freshwater macroinvertebrate species, including D. magna , C. dubia , and Chironomus riparius . These toxicity values were recently reviewed by Fuchsman et al [24]. For example, 10th‐percentile 48‐h LC50 (acute toxicity) values for diCB are 2,100 and 12,000 μg/L for D. magna and C. riparius , respectively, and the 16‐d EC50 (chronic toxicity) value is 1,400 μg/L for D. magna .…”