Sex differences in contaminant concentrations of fish: a synthesis.
A comparison of whole-fish polychlorinated biphenyl (PCB) and total mercury (Hg) concentrations in mature males with those in mature females may provide insights into sex differences in behavior, metabolism, and other physiological processes. In eight species of fish, we observed that males exceeded females in whole-fish PCB concentration by 17 to 43 %. Based on results from hypothesis testing, we concluded that these sex differences were most likely primarily driven by a higher rate of energy expenditure, stemming from higher resting metabolic rate (or standard metabolic rate (SMR)) and higher swimming activity, in males compared with females. A higher rate of energy expenditure led to a higher rate of food consumption, which, in turn, resulted in a higher rate of PCB accumulation. For two fish species, the growth dilution effect also made a substantial contribution to the sex difference in PCB concentrations, although the higher energy expenditure rate for males was still the primary driver. Hg concentration data were available for five of the eight species. For four of these five species, the ratio of PCB concentration in males to PCB concentration in females was substantially greater than the ratio of Hg concentration in males to Hg concentration in females. In sea lamprey (Petromyzon marinus), a very primitive fish, the two ratios were nearly identical. The most plausible explanation for this pattern was that certain androgens, such as testosterone and 11-ketotestosterone, enhanced Hg-elimination rate in males. In contrast, long-term elimination of PCBs is negligible for both sexes. According to this explanation, males not only ingest Hg at a higher rate than females but also eliminate Hg at a higher rate than females, in fish species other than sea lamprey. Male sea lamprey do not possess either of the above-specified androgens. These apparent sex differences in SMRs, activities, and Hg-elimination rates in teleost fishes may also apply, to some degree, to higher vertebrates including humans. Our synthesis findings will be useful in (1) developing sex-specific bioenergetics models for fish, (2) developing sex-specific risk assessment models for exposure of humans and wildlife to contaminants, and (3) refining Hg mass balance models for fish and higher vertebrates.
U. S. Geological Survey, Great Lakes Science Center, 1451 Green Road, Ann Arbor, MI 48105 USA.
Charles P
CP
Madenjian
Annis Water Resources Institute, Grand Valley State University, 740 West Shoreline Drive, Muskegon, MI 49441 USA.
Richard R
RR
Rediske
U. S. Geological Survey, Wisconsin Water Science Center, 8505 Research Way, Middleton, WI 53562 USA.
David P
DP
Krabbenhoft
U. S. Geological Survey, Great Lakes Science Center, Lake Erie Biological Station, 6100 Columbus Avenue, Sandusky, OH 44870 USA.
Martin A
MA
Stapanian
University of Michigan, School of Public Health, 1420 Washington Heights, Ann Arbor, MI 48109 USA.
Sergei M
SM
Chernyak
Bureau of Laboratories, Michigan Department of Health and Human Services, 3350 North Martin Luther King Jr. Boulevard, Lansing, MI 48906 USA.
James P
JP
O'Keefe
Androgens; Bioenergetics models; Gonadosomatic index; Gross growth efficiency; Hg-elimination rates; Laboratory mice; Teleost fishes; Testosterone; Vertebrates