Examination of temporal DDT trends in Lake Erie fish communities using dynamic linear modeling

The industrial pesticide dichlorodiphenyltrichloroethane (DDT) was initially heralded for its effectiveness against malaria and agricultural pests, but was eventually banned in North America during the 1970s due to growing concerns about its detrimental impacts on wildlife. Despite the successful termination of its commercial application, the persistent and bioaccumulative nature of DDT has resulted in lingering concentrations in aquatic food webs, particularly in upper trophic-level fish species. In this study, we used dynamic linear modeling to examine temporal trends of four DDT compounds (p,p′-DDT, o,p′-DDT, p,p′-DDE, and p,p′-DDD) in nine fish species in Lake Erie from 1976 to 2007, while considering both fish length and lipid content as covariates. Our results indicate that the levels of both p,p′-DDT and o,p′-DDT have been decreasing, often to the detection limit, with slowing decline rates during the second half of the study period. The p,p′-DDE levels were much more variable, exhibiting large fluctuations through time (though usually with a net downward trajectory), with the annual rates of change of the corresponding concentrations remaining negative or (more recently) near zero. Similarly, p,p′-DDD levels fluctuated (though to a lesser degree) over time, with gradually slowing decline rates in many fish species, such as smallmouth bass and freshwater drum. The results are in agreement with our understanding that DDE and DDD are degradation products of p,p′-DDT, and thus continue to be produced, as DDT is broken down. Declining trends observed for nearly all congeners and fish species indicate reduction of DDT risks in the Lake Erie fish communities.