Stable isotope ratios and contaminant concentrations in a sewage-distorted food web

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Abstract
Concentrations of selected neutral organic contaminants and stable isotope ratios of carbon, nitrogen and deuterium/hydrogen in invertebrates and fish were compared from near a large, 60 m deep municipal waste outfall near Los Angeles, California, [USA] where waste has a measurable influence on the structure of the marine food web, and from a reference area off Santa Barbara, California. Objectives were to investigate (1) the degree of utilization of sewage organic matter in the food web, especially by 3 species of fish, (2) differences in contaminant accumulation between these benthophagous fish and (3) the behavior of organic contaminants relative to each other and to organic matter through several trophic levels. Isotopically lighter carbon and nitrogen and higher concentrations of most chlorinated hydrocarbons were found in tissues of organisms from near the outfall. On the basis of the .delta.13NC and .delta.15N of the fishes, the estimated contribution of nitrogen and carbon from sewage was about 15 to 20% of their requirements for these elements. The .delta.13C and .delta.15N values increased in the fishes in the order of Microstomus pacificus. Citharichthys sordidus and Zaniolepis latipinnis. The Cs/K ratio of the latter species was also significantly higher than the former 2 species, also indicating its higher trophic position. C. sordidus had the highest wet-weight concentrations of chlorinated hydrocarbons and phthalic acid esters; intermediate concentrations of these compounds were found in Z. latipinnis and the lowest concentrations were found in M. pacificus. Concentrations of chlorinated hydrocarbons on a lipid-weight basis changed this order so that it more closely resembled the trophic structure revealed by the stable isotope ratio and Cs/K ratio data. Increases of both .DELTA.DT and Aroclor 1254, from deposit-feeding invertebrates through fish, were evident in foodwebs of the outfall and reference areas as positive correlations with .delta.13C. A large degree of correlation was evident between contaminants in Z. latipinnis but not in the other 2 fish species. These correlations were apparently not a function of liver lipid concentration, but the strengths of the correlations were dependent on the similarities of log Kow values of the correlated compounds.