Bioconcentration, biotransformation, and elimination of polycyclic aromatic hydrocarbons in sheepshead minnows (Cyprinodon variegatus) exposed to contaminated seawater

Sheepshead minnows (Cyprinodon variegates) were continuously exposed to two concentrations of polycyclic aromatic hydrocarbons (PAHs) dissolved in seawater (Sigma PAH = 7.57 and 72.31 mug/L) for 36 d, followed by 8 d of depuration. The PAHs studied were naphthalene (NPH or C-0-NPH), phenanthrene (PHE or C-0-PHE), pyrene (PYR), 2-methylnaphthalene (C-1-NPH), 1,3-dimethylnaphthalene (C-2-NPH), 2-isopropylnaphthalene (C-3-NPH), 9-methylphenanthrene (C-1-PHE), and 9-ethylphenanthrene (C-2- PHE). Uptake rate constants (k(1)) for NPHs increased with increasing degree of alkylation and log value of the octanol/water partition coefficient (K-ow), whereas k(1) values for three- and four-ring PAHs were lower despite their high log K-ow values. Elimination rate constants (k(2)) for the homologue series of NPHs and PHEs generally increased with decreasing degree of alkylation and log K-ow values. However, the depuration time did not directly correlate with the molecular size for nonalkylated PAHs. Bioconcentration factors (BCFs) were estimated from the ratio of k(1) to k(2) and also directly from PAH concentrations in fish tissue and water samples, and the factors generated by the two methods were very similar. A significant positive correlation was determined between log BCFs and log K-ow values for the series of C-0- through C-3-NPH at both low (r(2) = 0.985, p = 0.0077) and high (r(2) = 0.956, p = 0.022) exposures, although this correlation was not determined for all the PAHs studied. As a result of increased metabolism and/ or reduced bioavailability with increasing lipophilic character, the estimated BCFs for C-0- through C-2-PHE and PYR were generally lower than those for C-0- through C-3-NPH. The two exposure levels revealed minor variations in k(1) and k(2) values for parent PAHs and in the temporal pattern of PAH metabolite concentrations in bile. The present results indicate that the presence and nature of alkyl groups have a significant influence on the kinetics and metabolism of PAHs in fish.