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Comparative (Photoenhanced) Toxicity of Homocyclic and Heterocyclic PACs

2002; Taylor & Francis; Volume: 22; Issue: 3-4 Linguagem: Inglês

10.1080/10406630290103771

1563-5333

Eric A.J. Bleeker, Barry J. Pieters, Saskia Wiegman, Michiel H.S. Kraak,

Pharmaceutical and Antibiotic Environmental Impacts

Azaarenes are a group of heterocyclic PACs in which one carbon atom has been replaced by one nitrogen atom.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 heterocyclic analogues. Consequently, this difference in toxicity between both groups of compounds disappeared when the comparison was based on log K ow . Higher than predicted toxicities of both azaarenes and homocyclic PAHs were clearly related to photoenhanced toxicity. Especially anthracene and acridine showed strong increases in toxicity in the presence of UV radiation. This photoenhanced toxicity can accurately be predicted by the HOMO-LUMO gap values of the compounds. Therefore, it is concluded that extension of the present log K ow based QSARs with a descriptor for photoenhanced toxicity (such as the overlap between the absorption spectrum of the chemicals and the irradiance emitted by the light source used) appears to be a necessity for predicting toxicity of PACs in the environment.