The effects of xenobiotics are covered both in Option B Biochemistry & the environment  and in Option A Environmental impact - plastics. The presence of persistent organic pollutants (POPs) in the common tern (Sterna hirundo) in the Great Lakes ecosystem in the US has been studied by scientists from The State University of New York Buffalo.

Common tern ( Sterna hirundo )

( Image © Michiel Oversteegen, https://macaulaylibrary.org/asset/170211211 )

These persistent pollutants accumulate in the food chain through biomagnification and play a role in the decline of bird species due to their fish intake. The recent  studies show that pollutants which have been banned for many years are still present in the birds and causing the species to decline. They include polychlorinated biphenyls, PCBs, dichlorodiphenytrichlorethane, DDT, and other persistent pollutants such as polybrominated diphenyl ethers, PBDEs.

DDT (dichlorodiphenyltrichloroethane)

PCBs were banned in the US in 1978, and by the Stockholm Convention on Persistent Organic Pollutants in 2001. DDT has been banned in the US since 1972 and banned worldwide for agricultural use since 2004.  The sale and use of PBDEs has been banned or restricted in many parts of the  world since the beginning of this century. The legacy of all these different persistent pollutants clearly lasts for many years after their use has been banned.