Growth and development

PAHs have been shown to inhibit growth in a number of species. Some studies on fish have reported growth inhibition or changes to physiological parameters associated with energy allocation at low exposure concentrations. Sublethal responses for fish have been found at doses occurring as low as 0.1-1.0 mg total PAH/g fish/day. Interestingly, recent research reports alterations to several growth-related functions in fish (e.g., lipid content and metabolic enzymes), indicating that PAHs can cause a starvation syndrome even though the rate of food ingestion is not affected.

A few studies have examined growth effects for invertebrates. Studies with an earthworm (Eisenia veneta) exposed to eight different PAHs reported that most of the ECio values were around 30 mg/g dry weight of soil. For comparison to other studies, such as those above for fish, the ingestion rate and uptake efficiency of the PAHs from the ingested soil would have to be known. Another study reported dramatic reductions in the response concentration (several thousand-fold) when growth was assessed in juvenile bivalves (Mulinia lateralis) exposed to individual PAHs in combination with UV radiation (as compared to the response to PAHs without UV). In that study, only minor effects were observed when exposed to various petroleum products, indicating that these complex mixtures do not contain sufficient levels of the most phototoxic PAHs.

The effects on development due to PAH exposure have been studied in several species (mostly vertebrates), often reporting adverse responses at very low exposure concentrations. For example, one study reported several adverse effects (skeletal abnormalities, yolk sac edema, pericardial edema, genetic damage, and behavioral effects) in Pacific herring (Clupeapallasi) when eggs were exposed to crude oil for 16 days. These responses were observed at concentrations as low as 0.4ngml~ for 'weathered' crude oil, which is a natural process that results in the more volatile PAHs being lost, increasing the percentage of HPAHs and alkylated homologs. Recent work with zebrafish (Danio rerio) demonstrated that only some PAHs were able to induce a suite of developmental abnormalities that were triggered by a direct effect on cardiac function. The authors noted these effects for the PAHs dibenzothiophene and phenan-threne, but not for pyrene, which induced a different suite of adverse effects similar to those acting through the AhR.

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