Acute Photo-Induced Toxicity and Toxicokinetics of Single Compounds and Mixtures of Polycyclic Aromatic Hydrocarbons in Zebrafish

Newswise — Cincinnati, OH — This study aimed to investigate how exposure to multiple chemicals and stressors in the environment impact aquatic organisms polycyclic aromatic hydrocarbons (PAHs) are a class of chemical compound that are mainly found in oil and oil-type products. They are found in trace levels in most environments, but the highest exposures come from oil spills into aquatic environments. Because oil is a heterogeneous mixture of multiple compounds that includes PAHs, four compounds commonly found in oil spills were chosen.

Some PAHs also react when exposed to ultraviolet (UV) light, and become much more toxic. Due to this sensitizing effect, all tests were conducted under UV light to mimic sun exposure on a cloudless day. Certain organisms that are transparent or that have transparent life stages are much more susceptible to these effects than others. Because of this, translucent zebrafish larvae were selected as the test organism and were expected to represent a highly susceptible population.

The original plan was to choose two PAHs that reacted in UV light (were phototoxic) and two PAHs that were not, so that the tested mixture might represent an environmental exposure, such as an oil spill. However, when testing the compounds for toxicity, it became apparent that all four compounds were photo-reactive. This may mean that more PAHs than originally thought have this ability, and that their toxicity may have been underestimated previously if tests had not included UV exposure.

Lethal concentrations to 50% of the organisms (LC50s) were derived for each PAH individually, and then all combinations of mixtures were tested and compared to the individual results. Mixture toxicity tests found that the toxic effects were additive. For example, if 1 mg/L of PAH1 causes 10% mortality, adding 1 mg/L of PAH2 will increase toxicity to 20%. From this, all data were compiled, normalized based on potency (some had stronger effects than others), and a predictive model was developed. In this model, if the concentration of PAHs in an environmental exposure is known (oil spill), one can estimate the level of toxicity expected in susceptible organisms. Or, for use in remediation, the model can be used to protect organisms from toxic effects. Based on PAH concentrations found in water and circumstances of high UV dose to aquatic systems, there exists potential risk of photo-induced toxicity to aquatic organisms.

Ms. Alison Willis of TERA recently received her Master’s in Environmental Toxicology from Miami University. This work was done as her Master’s research and was recently published.

Willis, A.; Oris, JT. (2014). Acute photo-induced toxicity and toxicokinetics of single compounds and mixtures of polycyclic aromatic hydrocarbons in zebrafish. Environmental Toxicology and Chemistry. 33( 9): 2028–2037. Available online at http://onlinelibrary.wiley.com/doi/10.1002/etc.2648/abstract