there is considerable amount of 1 concerning the environmental impacts that animal 2 have on surface water. higher concentrations of hormones in waterways have been found to cause 3 and sexual impairment（损伤） in fish and other 4（水生的） species. however, a study from the university of delaware that examined estrogen（雌性激素） concentrations runoff from agricultural fields 5 with chicken 6（鸡粪） found that it is as much about the application of the manure as it is about the measurement of the types of estrogen. the study was conducted on the experimental plots on the 7 plain agricultural soils in middletown, de. it measured and compared the amounts of both 8, free forms of estrogen hormones and less toxic species found in runoff. corn was planted as a cover crop and chicken manure was 9 in either a pelletized（球状的） form or a raw litter form. reduced tillage（耕作，耕种） and no tillage treatments were also employed. samples of surface runoff were collected after 10 rain storms during the 2008 summer growing season from april through july.
sudarshan dutta, the author of the study, found that the amounts of estrogen were lower in plots fertilized with pelletized manure and plots that received no-tillage treatments.
additionally, dutta discovered the entire range of estrogen concentrations in the samples was significantly lower than those observed in other previous agricultural studies. nevertheless, concentrations of the less toxic 10（结合的） forms of estrogen were higher than the toxic, free forms.
according to dutta, prior studies did not usually measure the conjugate forms of estrogen, saying it is necessary to measure these forms.
"the higher concentration of conjugate forms of estrogens underscores the need for reporting all forms of the hormones. this is especially critical considering that conjugate species can be converted to the toxic free forms under certain environmental conditions," he says.
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