Comparative (Photoenhanced) Toxicity of Homocyclic and Heterocyclic PACs

Abstract

Azaarenes are a group of heterocyclic PACs in which one carbon atom has been replaced by one nitrogen atom. Heterocyclic PACs commonly occur in the environment, but risk assessment for PACs is solely based on (a small number of) homocyclic compounds. In order to examine whether the present risk assessment accurately protects against a broader range of PACs, the aim of this study was to compare the toxicity of an analogue series of homocyclic and heterocyclic PACs to a representative benthic invertebrate, the midge Chironomus riparius. The present study focused on generating toxicity data (96 h LC 50 ) for naphthalene, anthracene, phenanthrene, and pyrene to allow a comparison with previously obtained results for azaarenes. Since photoenhanced toxicity was expected for some of the compounds tested, experiments were carried out with and without a UV filter in order to obtain a complete assessment of the toxic mechanisms involved. Toxicity of homocyclic PAHs and azaarenes increased with increasing number of rings. In general, homocyclic PAHs were more toxic than their N-heterocyclic analogues, but homocyclic PAHs also are more lipophilic than their heterocyclicThe authors thank the Dutch Ministry of Housing, Spatial Planning and the Environment for its financial support.

Chronic toxicity of polycyclic aromatic compounds to the springtail Folsomia candida and the enchytraeid Enchytraeus crypticus

“…For both organisms, the inverse log‐transformed LC50 values showed a positive relationship with the log K ow of the test compounds. Bleeker et al [29] tested a series of PACs on larvae of the midge Chironomus riparius in a 96‐h aquatic toxicity test. In Figure 2, the relationship between LC50 data and log K ow from the acute aquatic toxicity tests by Bleeker at al.…”

“…In Figure 2, the relationship between LC50 data and log K ow from the acute aquatic toxicity tests by Bleeker at al. [29] is presented as a gray line, with the corresponding 95% confidence limits as dotted lines. The plot shows that for those PACs that do exert toxicity in the present study, the effect concentrations for F. candida generally are well described by the relationship obtained for the midge C. riparius , whereas E. crypticus clearly is less sensitive than F. candida and C. riparius (see discussion below).…”

“…Data for Folsomia candida are represented by squares, and data for Enchytraeus crypticus are represented by triangles. In both graphs, the solid line and the dotted lines represent the linear trend between 96‐h LC50 data and K ow and the 95% confidence intervals, respectively, obtained from water‐only exposure of midge larvae to similar PACs [29].…”

Acute photo‐induced toxicity and toxicokinetics of single compounds and mixtures of polycyclic aromatic hydrocarbons in zebrafish

“…Physical characteristics used as predictors of toxicity include number of benzene rings, octanol–water partition coefficient ( K OW ), solubility in water, chemical stability, and others . However, photo‐induced toxicity deviates from some of traditional predictive physical properties and shifts to other properties . Many studies have identified QSAR predictors for photo‐induced toxicity, including molecular size, lipid partitioning coefficients, and other intermolecular forces such as molecular polarizability or E gap (electronic structural property related to the ability for UV absorption) .…”

“…Many studies have identified QSAR predictors for photo‐induced toxicity, including molecular size, lipid partitioning coefficients, and other intermolecular forces such as molecular polarizability or E gap (electronic structural property related to the ability for UV absorption) . It is widely reported in the literature that a HOMO‐LUMO gap in the range of 7.1 ± 0.4 eV is an indicator of potential for photo‐induced toxicity . The HOMO‐LUMO gaps for anthracene and pyrene are within this range; however, phenanthrene and carbazole are outside this range.…”