by Grace Reckers
Polychlorinated biphenyls (PCBs) are a class of thermodynamically stable and lipophilic molecules that have been used throughout twentieth century industrialized projects. They have become a major topic of environmental concern for their persistence in sediments and contamination qualities that are hard to reverse. Their ability to imbed in sediments as toxic substances and resist rapid degradation have made it challenging to remove the molecules (each categorized as one of 209 ‘congeners’) and to eliminate their long-term toxic effects from the sediment they persist in. However, these qualities have also enabled scientists to examine historical levels of PCB usage by taking samples of varying sediment depths and recording changes in PCB concentration.
Wafo et al. (2016) used sampling extraction and chemical analysis methods to map out the distribution of PCBs in the Toulon Bay of the southern coast of France. The bay has two naturally connected yet artificially distinct components: one smaller, more shallow, protected bay that has experienced heavy traffic from tourists, industrialization, and other pollutants; and one larger, deeper bay that is more exposed to the external ocean and less frequented by human polluting sources. A pier constructed in the Toulon Bay harbor has further separated the two bays. Wafo et al. extracted samples of sediments from 39 locations throughout Toulon Bay at three different times over the course of eight months. Cylindrical tubes of 10 cm in length were inserted into these 39 sediment locations to measure granule concentrations measured in mg kg-1 of congeners for different lengths each sample. These cylindrical tube samples were further divided into measures taken from 0-5 cm and those taken from 5-10 cm. The distribution of PCBs in the Toulon Bay was then analyzed and mapped out in terms of trends in concentration at varying depths, and comparisons were made between other regions to determine Toulon Bay’s relative levels of contamination, the greater historical spread of PCBs, what the sources of contamination may be, and to estimate the effects of their toxicity.
These comparisons were made between samples from both bays and with the open ocean to gauge the relative concentrations of PCBs in the Toulon Bay versus the standard amount in an exposed body of water without dense human activity. They were also made between other coastal areas. Wafo et al. found highly homogenous levels of PCB concentrations throughout different depths, indicating a constant presence of PCB contaminating sources throughout the historical time period, noting some changes in concentrations at predicted eras, such as the increase in PCB contamination during a battle in 1942 and the decrease in observed levels after France banned PCBs in 1986. Overall, the smaller bay had greater concentrations of congeners observed at each depth due to a greater exposure to human activity and pollutants in a concentrated area. The larger bay had lesser-observed concentrations of PCBs throughout the chronological eras, presumably because of less human and industrialized interaction and more water flow with the open sea.
Despite congener concentrations at times reaching greater than 2530 ng g-1 at some locations in the Toulon Bay, indicating high environmental concern, the larger bay had levels not indicating environmental concern, averaging 1.9 – 136 ng g-1. Furthermore, these concentrations are comparable to levels recorded at other sites listed in the study. As the decrease in use of PCBs continues since the 1980-1990s, scientists and other environmental activists hope that the concentrations of congeners found at upper levels of sediment samples remain low.
Wafo, E., Abou, L., Nicolay, A., Boissery, P., Perez, T., Ngono Abondo, R., Garnier, C., Chacha, M, Portugal, H., 2016. A chronicle of the changes undergone by a maritime territory, the Bay of Toulon (Var Coast, France), and their consequences on PCB contamination. SpringerPlus 5, 1230-1244 https://springerplus.springeropen.com/articles/10.1186/s40064-016-2715-2.