Which class of pesticides is associated with eggshell thinning and estrogenic effects in birds?

• A. Organochlorine pesticides
• B. Organophosphate pesticides
• C. Carbamates
• D. Pyrethroids

Answer: (A)

Eggshell thinning and estrogenic effects in birds point to exposure to persistent pesticides that disrupt endocrine signaling and accumulate in tissues. The hallmark compounds are organochlorines, such as DDT and its breakdown products, which resist degradation and build up in the food chain. When birds ingest these residues, they concentrate in the eggs and interfere with calcium deposition in the shell gland, producing thinner eggshells that are more likely to break before hatching. At the same time, these chemicals can act as estrogenic disruptors, altering hormonal regulation of reproduction. Other pesticide classes—organophosphates and carbamates—primarily cause acute nervous system toxicity by inhibiting acetylcholinesterase and do not have the same persistent, endocrine-disrupting effects. Pyrethroids are mainly neurotoxic with less emphasis on long-term reproductive disruption. Hence, the association is with persistent organochlorine pesticides.