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

Abstract

An urgent need exists for incorporating heterocyclic compounds and (bio)transformation products in ecotoxicological test schemes and risk assessment of polycyclic aromatic compounds (PACs). The aim of the present study therefore was to determine the chronic effects of (heterocyclic) PACs on two terrestrial invertebrates, the springtail Folsomia candida and the enchytraeid Enchytraeus crypticus. The effects of 11 PACs were determined in chronic experiments using reproduction and survival as endpoints. The results demonstrated that as far as narcosis-induced mortality is concerned, effects of both homocyclic and heterocyclic PACs are well described by the relationship between estimated pore-water 50% lethal concentrations and log Kow. In contrast, specific effects on reproduction varied between species and between compounds as closely related as isomers, showing up as deviations from the relationship between pore-water 50% effect concentrations and log Kow. These unpredictable specific effects on reproduction force one to test the toxicity of these PACs to populations of soil invertebrates to obtain reliable effect concentrations for use in risk assessment of PACs.

Life cycle responses of the midge Chironomus riparius to polycyclic aromatic compound exposure

“…Consequently, deviations from the relationship between effect concentrations and K ow values may indicate a different mode of action (Bearden and Schultz, 1998;Escher et al, 2005). This was clearly demonstrated previously for soil invertebrates chronically exposed to several PACs (Sverdrup et al, 2001;Droge et al, 2006), and therefore in the present study we followed the same approach. Since for the tested compounds, having a logK ow value <5, porewater exposure of the midge larvae was expected (Belfroid et al, 1996), chronic LC 50 values (mM) were calculated from the chronic sediment LC 50 values (mmol/kg sediment d.w., Table 2), using a set of empirically determined organic carbon-water partition coefficients (K oc ) from (Jonassen, 2003;Jonassen et al, 2003) and correcting for the organic carbon content of the sediment.…”

“…In those acute high-dose experiments, narcosis was the main mode of action. The lower limit for narcosis was estimated by dividing the acute LC 50 values from the LC 50 elogK ow relationship by a factor of 3, because in previous studies on soil invertebrates a LC 50 / EC 50 ratio larger than 3 suggested sublethal effects of the tested compounds on reproduction, deviating from narcosis (Droge et al, 2006). Hence, we assumed that specific effects on emergence occurred if the effect concentrations obtained in the present study were below the calculated lower limit for narcosis.…”

“…Azaarenes and their transformation products, more polar than their homocyclic analogues, can interact specifically with cell membranes and DNA, and this interaction may influence their toxicity (De Voogt et al, 1999). Since isomer specific toxicity of PACs has been established in several studies (Kraak et al, 1997;Bleeker et al, 1999a;De Voogt et al, 1999;Wiegman et al, 2001;Droge et al, 2006), three isomer pairs were selected: two three-ringed homocyclic compounds, two three-ringed azaarenes and the two main transformation products of the two azaarenes. The aim of this study was to determine if the closely related homo-and heterocyclic compounds affected emergence of the midge Chironomus riparius during chronic exposure to PAC spiked sediments.…”

Comparative chronic toxicity of homo- and heterocyclic aromatic compounds to benthic and terrestrial invertebrates: Generalizations and exceptions

“…This generalization is obviously a big step forward, but the same study demonstrated that specific modes of action other than narcosis caused strong deviations from the relationship between toxicity and logK ow (Bleeker et al, 2002a). Such specific modes of action may even cause closely related compounds, such as isomers, to differ several orders of magnitude in toxicity (Walton et al, 1983;Wood et al, 1983;Kraak et al, 1997;Wiegman et al, 2001;Bleeker et al, 2002a;Droge et al, 2006;León Paumen et al, 2008a). Comparative toxicity is further complicated by the repeated observations that transformation products, generated with the aim to detoxify the parent compound, may have an unexpected and sometimes even exceptionally high toxicity.…”

“…In many short-term high-dose PAC toxicity studies, including those mentioned above, mortality was used as endpoint. This ignores that PACs can exert sublethal effects during long-term exposure, therewith affecting different biological endpoints (Droge et al, 2006;Feldmannova et al, 2006;León Paumen et al, 2008a). Hence, a reliable hazard assessment for PACs requires the inclusion of biological endpoints other than mortality, such as chronic effects on growth and reproduction.…”