Examining the correlation between quantifiable SVOCs and organic carbon content or particulate size in benthic sediments as a function of ocean stratum

Abstract

The raw analytical concentration values of semi-volatile organic compounds (SVOCs) in ocean sediments do not necessarily reflect the bioavailable fractions of SVOCs in the sediments due to factors such as the total organic carbon content of sediments (TOC) and the percentage of fine particles in sediments (% fines) as they are believed to affect the extraction efficiency of SVOCs from sediments. Corrective actions are therefore taken to minimize their influence on measurements. In doing so, a broad and uniform correlation is assumed to exist between the ‘native’ levels of SVOCs and TOC or % fines across ocean strata. However, the validity of this blanket assumption is not yet verified. In this study, we examined the strength of the assumption using DDTs, PAHs and PCBs levels in sediments from Santa Monica Bay (SMB), California, USA. (The distribution patterns of these SVOCs in SMB are known and reproducible for quality assurance.) As our results show, a uniform correlation between SVOC levels and TOC or % fines across strata is mostly absent. For example, PAH and PCB levels show negative correlation with TOC or % fines, and only in canyon sediments, DDT levels correlate positively with both TOC and % fines across at least three strata. Furthermore, the distribution of PAH molecules appears to be controlled by molecular size with smaller PAHs being found almost exclusively in the canyons. Our finding here, being the first of its kind, suggests that more work is needed to clarify the reporting of SVOC levels in ocean sediments.