In the bodies of reptiles, some industrial by-products cause elevated hormonal activity. Hormones govern the development of certain body parts, and in reptiles abnormal development of these parts occurs only with elevated hormonal activity. Recently, several alligators with the telltale developmental abnormalities were discovered in a swamp. So, apparently, industrial by-products have entered the swamp' s ecosystem.
The reasoning in the argument is most vulnerable to criticism on the grounds that the argument provides no explanation for developmental abnormalities that do not result from elevated hormonal activity.