P450 aromatase alterations and DNA damage as avian pollution biomarkers in cliff and cave swallow breeding near the Rio Grande region, Texas
Sitzlar, Megan Annette
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The endocrine system, specifically relating to sex hormones, and genetic material can be targets of environmental contaminants. Environmental contaminants in the Rio Grande region may originate from industrial or agricultural processes and growing populations lacking proper water and sewage infrastructure. Cliff (Petrochelidon pyrrhonota) and cave (P. fulva) swallows breeding near the Rio Grande were selected to monitor aromatase activity alterations and DNA damage. Swallows were sampled at six sites along the Rio Grande from Brownsville to Laredo, and a reference site (Somerville) 350 miles north of the Rio Grande. DNA damage, based on nuclear DNA content, was determined by flow cytometry. A significantly larger mean half peak coefficient of variation (HPCV) of DNA content in contaminated sites compared to a reference site reflects possible chromosomal damage. No detectable HPCV differences were observed in cave swallows among locations, notwithstanding the presence of mutagenic contaminants. Selenium may provide a protective role against genetic damage. However, cliff swallows from Laredo had significantly higher HPCV values than those from Somerville. DNA damage could be attributed to metals and polycyclic aromatic hydrocarbons released near Laredo. Brains and gonads, two estrogen-dependent organs, were tested for aromatase activity with a tritiated water method. Brain aromatase activity was higher, though not always statistically, for male cave and male and female cliff swallows. Dichlorodiphenyldichloroethylene (DDE) may play a role in the increased activity. Female cave swallows in Llano Grande appeared to have a greatly depressed brain aromatase activity, possibly attributed to past human use of toxaphene. Testicular and ovarian aromatase activity in cliff and cave swallows from Rio Grande was higher than in those from Somerville, though not always significantly. DDE, atrazine, sewage treatment plant contaminants (phthalates, alkylphenols, ethynylestradiol), metals, or other pollutants could play a role in the increased gonadal activity. Increased aromatase activity, in association with contaminants, may be easier to detect in testes of male birds which normally exhibit low levels of estrogen. Siterelated contaminants may be playing a role in DNA damage and aromatase alterations. This is the first known study which uses aromatase activity as an endocrine disruptor indicator in wild birds.