Recent concerns about a potential release of DDT due to extreme rain events, such as the storms during the winter of 2023, led to an effort to collect water samples from the Pajaro River. Back in 1995, the Pajaro River flooded into nearby Elkhorn Slough, and subsequently Caspian terns suffered a reproductive failure (Parkin 1998), which was deemed due to much higher DDT concentrations found in the eggshells that year. DDT is well known for thinning eggshells, and is considered a legacy pollutant that periodically becomes remobilized via sediment movement, such as extreme weather events and flooding.
Scientists concerned that the 1995 calamity might repeat in 2023 mobilized to test for legacy pollutants and current-use pesticides after the Pajaro River levee breached in March 2023. As in 1995, flood waters again flowed into ESNERR in 2023. Samples of Pajaro River flood water were collected at four sites upstream of ESNERR in March 2023 and sent to two labs for analysis of DDT and several other chemicals. As expected, DDT and other chemicals were readily detected. It remains to be seen whether birds nesting in the area will again be adversely affected by legacy DDT.
Despite being banned from use in the United States since 1972, DDTs remain a prominent environmental concern. Recent hatching failures of Central California Condors have been linked to DDT accumulated in the blubber of beach-cast marine mammal carcasses consumed by the birds (Burnett et al. 2013, Stack et al. 2022). Within the Monterey Bay area, the Central Coast Long-term Environmental Assessment Network (CCLEAN) has found that loads of legacy contaminants are orders of magnitude greater from rivers than from municipal wastewater discharges and summed DDT loads from rivers over the last two decades have exceeded 145 Kg.
Literature Cited:
Burnett, LJ, KJ Sorenson, J Brandt, EA Sandhaus, D Ciani, M Clrk, C David, J Theule, S Kasielke, RW Risebrough. 2013. Eggshell thinning and depressed hatching success of California Condors reintroduced to Central California. The Condor. 11(3): 477-491.
Parkin, JL. 1998. Ecology of breeding Caspian terns (Sterna caspia) in Elkhorn Slough, California. M.S. Thesis, San Jose State University, https://scholarworks.sjsu.edu/etd_theses/1663
Stack, ME, JM Cossaboon, CW Tubbs, LI Vilchis, RG Felton, JL Johnson, K Danil, G Heckel, E Hoh, NG Dodder. 2022. Assessing marine endocrine-disrupting chemicals in the critically endangered California Condor: Implications for reintroduction to coastal environments. Environmental Science & Technology. 56: 7800-7809.