Toxicity of Polycyclic Aromatic Hydrocarbons to the Nematode Caenorhabditis elegans

Abstract

The presence of polycyclic aromatic hydrocarbons (PAHs) in the environment has attracted much concern owing to their mutagenic and carcinogenic properties. Regulatory authorities have favored the use of biological indicators as an essential means of assessing potential toxicity of environmental pollutants. This study aimed to assess the toxicity of acenaphthene, phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene to Caenorhabditis elegans by measuring LC50 and EC50 values for growth and reproduction. The exposure to all chemicals was carried out in aqueous medium. All PAHs showed a low acute toxicity to C. elegans. There was no significant mortality in C. elegans after 24 h of exposure at PAH concentrations within (and indeed above) their respective solubility limits. Prolonged exposure (72 h) at high concentrations for acenaphthene (70,573 μg/L), phenanthrene (3758 μg/L), anthracene (1600 μg/L), fluoranthene (1955 μg/L), pyrene (1653 μg/L), and benzo[a]pyrene (80 μg/L) produced mortality. Results also showed that reproduction and growth were much more sensitive parameters of adverse response than lethality, and consequently may be more useful in assessing PAH toxicity using C. elegans. In comparison with previous studies, C. elegans was found to be approximately 2-fold less sensitive to acenaphthene, 5-fold less sensitive to phenanthrene, and 20-fold less sensitive to fluoranthene than Daphnia magna. However, the 48-h LC50 for benzo[a]pyrene (174 μg/L) reported in the present study with C. elegans was similar to that reported elsewhere for Daphnia magna (200 μg/L). Although C. elegans indicated greater sensitivity to benzo[a]pyrene than Artemia salina (174 μg/L vs. 10000 μg/L), the organism showed less sensitivity to pyrene (8 μg/L vs. 2418 μg/L), fluoranthene (40 μg/L vs. 2719 μg/L), and phenanthrene (677 μg/L vs. 4772 μg/L) than Artemia salina. Caenorhabditis elegans, while not the most sensitive of species for PAH toxicity assessment, may still hold applicability in screening of contaminated soils and sediments.

Acknowledgements

We express our appreciation to Angela Maher, Judith Mayne, and Emma Knight for valuable assistance in the laboratory. We also thank Professor Phillip Williams of Environmental Health Science, Georgia Institute of Technology, and Dr. Albert L. Juhasz of the Adelaide laboratory, University of South Australia, for helpful supply of source materials at the initial stages of this study. The gifts of Caenorhabditis elegans and Escherichia coli cultures from the Caenorhabditis Genetics Centre, Minnesota, are gratefully acknowledged. This research was sponsored (through a PhD studentship) by the Bayelsa State Government of Nigeria. The authors also acknowledge contributions from two anonymous referees who provided useful suggestions that enabled significant improvement of the article.