TOXICITY AND TOXICOKINETICS OF BINARY COMBINATIONS OF PETROLEUM HYDROCARBON DISTILLATES WITH THE EARTHWORM EISENIA ANDREI

Abstract

Petroleum hydrocarbons (PHCs) act via narcosis and are expected to have additive toxicity. However, previous work has demonstrated less-than-additive toxicity with PHC distillates and earthworms. A study was initiated to investigate this through toxicity and toxicokinetic studies with the earthworm Eisenia andrei. Three petroleum distillate fractions, F2 (>C10-C16), F3a (>C16-C23), and F3b (>C23-C34), were used in two binary combinations, F2F3a and F3aF3b. In the toxicity study, clean soil was spiked with equitoxic combinations of the two distillates ranging from 0.5 to 2.5 toxic units. In the toxicokinetic study, a binary combination consisting of one concentration of each distillate was used. On a soil concentration basis, the toxicity of the binary combinations of distillates was less than additive. Accumulation of the individual distillates, however, was generally reduced when a second distillate was present, resulting in lower body burden. This is thought to be due to the presence of a nonaqueous-phase liquid at the soil concentrations used. On a tissue concentration basis, toxicity was closer to additive. The results demonstrate that tissue concentrations are the preferred metric for toxicity for earthworms. They also demonstrate that the Canada-wide soil standards based on individual distillates are likely protective.

Petroleum hydrocarbon mixture toxicity and a trait‐based approach to soil invertebrate species for site‐specific risk assessments

“…Concentration addition overpredicted F2 mortality, and independent action overpredicted both F2 mortality and reproduction. The ranges in values predicted by concentration addition and independent action for F2 mortality for earthworms were 1464 to 1593 mg/kg and 1317 to 11 434 mg/kg F2, respectively, whereas the ranges we found in the literature and the regulations were 237 to 776 mg/kg F2 (Energy Services Group International 2003; Canadian Council of Ministers of the Environment 2008; Cermak et al 2010Cermak et al , 2013Erlacher et al 2013; Table 3). The ranges in values predicted by concentration addition and independent action for F2 reproduction for all species were 32 to 2714 mg/kg F2 and 460 to 2504 mg/kg F2, respectively, whereas the ranges in the literature and the regulations for 2 species (E. andrei and O. folsomi) were 132 to 211 mg/kg F2 (Energy Services Group International 2003; Canadian Council of Ministers of the Environment 2008; Cermak et al 2010Cermak et al , 2013Erlacher et al 2013).…”

“…Both models underestimated the toxicity of F2 mortality, because the average literature values and regulatory values were below the lowest model-predicted F2 EC value (Figure 3 and Supplemental Data, Figure S-4). However, the toxicity endpoint values from the literature (Cermak et al 2010(Cermak et al , 2013Erlacher et al 2013;Agnell et al 2012) and regulations (Canadian Council of Ministers of the Environment 2008) were lower relative to the species we tested, because these data points reflected averages of 2 species (E. andrei and O. folsomi), with the earthworms being a species sensitive to petroleum hydrocarbon-contaminated soils.…”

“…Other studies on toxicants with similar and dissimilar mechanisms of action found comparable results, that is, independent action and concentration addition fit observed mixture toxicity data similarly (Faust et al ; Backhaus et al ; Cedergreen et al ; Mo et al ; Schnug et al ; Qiu et al ). Of the limited studies on binary petroleum hydrocarbon mixture toxicity to soil invertebrates, Cermak et al () found that mixtures of F2 and F3 petroleum hydrocarbon followed concentration addition based on earthworm organism tissue concentration. However, on a soil concentration basis, antagonism was observed, likely due to decreased bioavailability from preferential partitioning to nonaqueous phases in soil (Cermak et al ).…”

“…Analysis of the dose response of soil invertebrates to the mixture followed guidance recommended by Environment Canada (2005 Table S-3) were estimated from either available literature studies conducted with singlesubstance petroleum hydrocarbon distillates on similar species (Cermak et al 2010(Cermak et al , 2013Erlacher et al 2013) or the regulatory estimated species sensitivity distribution (SSD) for ecological soil contact when no available literature for single-substance toxicity endpoints existed (Canadian Council of Ministers of the Environment 2008; Supplemental Data, Tables S-4 and S-5). For the mite species, the mortality value was assumed to be double the estimated SSD to account for higher values observed for mortality.…”

“…Furthermore, single‐component toxicity testing for assessing toxicity to soil invertebrates and plants uses a constant 4:1 aliphatic:aromatic petroleum hydrocarbon ratio (Canadian Council of Ministers of the Environment ). Because many refined petroleum hydrocarbons have varying aliphatic:aromatic ratios and aromatics bioaccumulate more readily, toxicity to soil invertebrates and plants varies with petroleum hydrocarbon products (Cermak et al ). Although the current petroleum hydrocarbon remedial guidelines have drawbacks, such as lack of consideration of mixtures and variations in the composition of petroleum hydrocarbon products, the current petroleum hydrocarbon management framework reflects a tier 1 approach, with the generalizations needed to manage a range of contaminated sites.…”