Dr. Johan Liebens

In a contaminant study of surface sediments performed in Escambia Bay, Florida, in 2009, DDT was present in 13 of 30 tested sites that were located in the wetlands adjacent to the bay. Concentrations were well above the Florida Department of Environmental Protection's Probable Effect Level (PEL), and ratios of DDT and its metabolites indicated a recent introduction to the system, despite the use of DDT having been banned in 1973. A follow-up study performed in 2016 found no DDT, but did show DDE (a DDT degradation product) at several sites. Spring 2017 sampling showed no DDT, DDE at five of six sampling sites and DDD (another DDT degradation product) at two of the six sites. The appearance of degradation products suggests that DDT degraded or sediment movement brought the degradation products to the sites. In spring of 2018, sediment cores were collected to assess subsurface contaminant concentrations at five sites that consistently had detectable concentration of DDT or its degradation products in previous years. The cores, ranging from approximately 0.2-0.8 meters in depth, were sampled based upon physical characteristics of the sediment. Two methods were used to extract and analyze for DDT and its byproducts from the sediments, a soxhlet extraction (EPA methods 3540c and 3620c) and a microwave extraction (EPA methods 3051a and 3546). Extracts were analyzed using gas chromatography (GC-ECD). Results show the presence of DDE at all five sites tested, DDD at three sites, and DDT at two sites, all at various depths. Of the five tested sites, three sites clearly exhibited decreasing DDE concentration with increased depth and one site exhibited the same decreasing trend but had high levels of DDE at the bottom of the core (>0.5 m depth). DDD showed a similar pattern, decreasing with depth at two of the three sites that is was detected at. There are no evident relationships between particle size and these trends. All samples with detections exceeded the TEL for DDE (17 samples) and DDD (7 samples) but not for DDT; two samples exceeded the PEL for DDD. The trend of generally decreasing concentration with depth of DDE and DDD suggest that the reworking of sediment is not the source of the contaminants. One site had high levels of DDE at depth but is downstream from the other sites and thus cannot be a source of the contaminants, DDT, DDE, or DDD.

Dichlorodiphenyltrichloroethane (DDT) was a commonly used pesticide from World War II through the 1960's. DDT is generally used to control mosquito populations and as an agricultural insecticide. The pesticide and its degradation products (DDD and DDE) can bioaccumulate within ecosystems having negative implications for animal and human health. Consequently, DDT usage was banned in the United States in 1973. In a contaminant study performed in Escambia Bay, Florida, in 2009, DDT was present in 25% of study sites, most of which were located in the upper bay wetlands. Concentrations were well above the Florida Department of Environmental Protection's (FDEP) Probable Effect Level (PEL) and ratios of DDT and its metabolites indicated a recent introduction to the system. A follow-up study performed in 2016 found no DDT, but did show DDE at several sites. The current study repeated sampling in May 2017 at sites from the 2009 and 2016 studies. Sediment samples were collected in triplicate using a ponar sampler and DDT, DDD and DDE were extracted using EPA methods 3540c and 3620c. Extracts were analyzed using a gas chromatograph with electron capture detection (GC-ECD) as per EPA method 8081c. Sediment was also analyzed for organic carbon and particle size using an elemental NC analyzer and a laser diffraction particle sizer. Results show the presence of breakdown products DDE and DDD at multiple sites, but no detectable levels of DDT at any site. Sampling sites with high levels of DDT contamination in 2009 show only breakdown products in both 2016 and 2017. Particle size has little influence on DDD or DDE concentrations but OC is a controlling factor as indicated for contaminated sites by Pearson correlations between OC and DDE and DDD of 0.82 and 0.92, respectively. The presence of only DDD and/or DDE in the 2016 and 2017 studies indicates that the parent, DDT, has not been re-introduced into the watershed since 2009 but is degrading in the environment.