Chronic Toxicity Thresholds for Sediment-Associated Benzo[a]pyrene in the Midge (Chironomus dilutus)

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in aquatic ecosystems and have been shown to be one of the causes of sediment toxicity to benthic invertebrates. Benzo[a]pyrene (BaP) was selected as a representative for the PAH family of compounds for developing chronic sediment toxicity thresholds for Chironomus dilutus. Life-cycle toxicity testing was initiated using newly hatched midge larvae and terminated until hatch of the second generation. Median lethal concentrations were 92.5 ± 19.6 and 56.9 ± 1.76 lg/g organic carbon (OC) after exposing midges to sedimentassociated BaP for 20 days (before pupation) and 43 days (end of test), respectively. Sublethal toxicity was described as 5 and 50 % effect concentrations (EC5 and EC50), and these were 6.63 ± 0.82 and 41.1 ± 1.61 lg/g OC for growth reduction at 20 days, respectively. Impairments of emergence and reproduction of C. dilutus were also assessed at the end of the testing, and the EC5 and EC50 values were 3.41 ± 0.53 and 26.9 ± 1.43 lg/g OC for emergence and 2.18 ± 0.34 and 13.4 ± 1.13 lg/g OC for reproduction, respectively. In addition, bioavailability-based chronic toxicity thresholds were also established using Tenax-extractable BaP concentrations. Although more environmentally relevant, data regarding chronic toxicity are less available than those regarding acute toxicity. Therefore, establishing numeric chronic toxicity thresholds for sediment-associated BaP with the consideration of the bioavailability would improve the accuracy of assessing PAH-related sediment toxicity.

Assessment of Sediment Risk in the North End of Tai Lake, China: Integrating Chemical Analysis and Chronic Toxicity Testing with Chironomus dilutus

“…3, fecundity of the midges decreased at site T1 (621 ± 191 eggs/female) relative to the control (872 ± 161 eggs/female) (p \ 0.05), but no significant difference in fecundity was noted for others sites. Similar to previous studies (Du et al 2013(Du et al , 2014, egg hatchability was not sensitive to sediment-bound contaminants, and [91 % of eggs were hatched after midges were exposed to all sediments. In summary, except for site T5, field sediments from Tai Lake were chronically toxic-such as attenuated survivorship, decreased growth, impaired emergence, and low fecundity-to C. dilutus.…”

“…Meanwhile, a control sediment was collected from a drinking-water reservoir in Conghua, China. This sediment exhibited no chronic toxicity to the midges and contained no target contaminants at concentrations greater than the reporting limits (RLs) (Du et al 2013(Du et al , 2014.…”

“…To estimate RTU of PAHs, the toxicity data of PAHs were first converted to benzo[a]pyrene (BaP) equivalents using (Du et al 2014). As shown in Table 1, the RTU of PAHs ranged from 0.12 in sediment T5 to 0.45 in sediments T2 and T3, thus suggesting that PAHs may partially contribute to the observed toxicity but that the contribution was relatively low.…”

“…The TUs of permethrin were calculated from its chronic EC 50 value for the emergence of C. dilutus (0.84 lg/g OC) (Du et al 2014). Because no chronic toxicity data are available for other PYRs, their chronic EC 50 values were deducted by dividing their acute LC 50 values by an ACR of 29.2, which was estimated from the toxicity data of permethrin.…”

Integrated sediment quality assessment through biomarker responses and bioavailability measurements: Application in Tai Lake, China

“…Assuming concentration addition for chemicals in the same class, joint toxicity was estimated as the sum of TU bioavailable of individual contaminants. Before computing the TU bioavailable of PAHs, chronic EC50 of individual PAHs were derived from the Tenaxbased EC50 of benzo[a]pyrene (BaP) for the emergence of C. dilutus (14.2 mg/g OC) (Du et al, 2014). The TEF values suggested by the USEPA (1993) were used to convert toxicity data of individual PAHs to their BaP equivalents.…”