Examining the potential for using unfrozen sediments in trace-level analysis of organic pollutants in the Santa Monica Bay

Poster Presentation

Prepared by O. Otim
Environmental Monitoring Division, City of Los Angeles, 12000 Vista Del Mar, Playa del Rey, California, 90293, United States

Contact Information: ochan.otim@lacity.org; 310-648-5835


The need to freeze ocean sediment samples on collection for trace-level analyses of anthropogenic semivolatile organic pollutants does not only pose a logistical challenge, but reduces the fidelity of data quality due to the concomitant loss associated with the freeze-thaw cycle during samples processing. In this study, we show that immediate sediment freezing may not be necessary in order to preserve the endogenous levels of dichlorodiphenyltrichloroethane pesticides (DDTs), polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs) in the sediments. Using split-paired Santa Monica Bay (SMB) sediment samples collected from 17 stations, we demonstrate that refrigerated sediment samples (4oC up to 11 days), in fact, contained more PCB congeners and PAHs in total than the frozen samples. The loss of PCB congeners due to freezing is statistically significant (F1,24 = 8.18, p < .05). The perceived loss of PAHs, although not found to be statistically significant (F1,28 = 4.01, p > .05), is shown not to lend support to freezing sediments as a way of preserving detectable PAHs in the SMB sediments under study. For the individual DDTs studied, not only were the means of each paired data found to be significantly related (r = 0.98, p < .01, degree of freedom: 111; rČ = 0.96), a strong agreement within each data pair was also shown to exist (limits of agreement: 0.22 ± 3.25 ug/kg). These results suggest that refrigeration at 4oC up to 11 days prior to processing has minimal effect on the levels and characteristics of the DDTs, the PCB congeners and the PAH in the Santa Monica Bay (SMB) sediment samples from the 17 stations. It is only fair then to suggest that DDTs, PCBs and PAHs data from SMB sediments handled similarly in future be considered as substitute for data from the frozen sediments.