Effect of aging on bioaccessibility of DDTs and PCBs in marine sediment

Abstract

Hydrophobic legacy contaminants like dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs) were banned almost half a century ago. While their residues still remain in many environmental compartments, they have undergone extensive aging and likely have lower bioaccessibility (the available fraction) compared to fresh residues. However, risk assessment relies heavily on the use of total chemical concentration, rather than accounting for age-diminished bioaccessibility, likely leading to overestimated risks. In this study, we used 24 h Tenax desorption to measure the potential bioaccessibility of DDTs and PCBs in two sediment cores taken from the Palos Verdes Shelf Superfund site in the Pacific Ocean. The total concentrations of DDTs and PCBs from the core located at the sewage outfall (8C) were as high as 41,000-15,700 μg/kg (dry weight, dw) and 530-2,600 μg/kg dw, respectively, while those from a location 7 km northeast of the outfall (3C) were 2-3 orders of magnitude lower. Bioaccessibility estimated by 24-h Tenax-aided desorption (F 24h ) decreased in the order of DDD > DDE > DDT for DDT derivatives, and PCB 52 > PCB 70 > PCB 153 for PCB congeners, showing a negative correlation with their log K ow . Due to the extensive aging, F 24h values were <20% of the total chemical concentration for most contaminants and <5% for DDT, DDE and PCB 153, suggesting that aging greatly diminished their bioavailability. However, a quantitative relationship between F 24h and sediment age along the vertical profile was not found, likely because the contaminant residues had undergone aging before their offsite transport and deposition onto the ocean floor. As the use of man-made chemicals such as DDT and PCBs was discontinued in the U.S. many decades ago, the reduction in their bioavailability due to aging may be universal and should be taken into consideration to avoid overly conservative risk predictions or unnecessary mitigation interventions.

Sediment contamination of an urban canal—a case study approach for an integrated assessment of organic sediment contamination

“…In comparison with reported concentration ranges in other regions, the canal sediments are highly contaminated, partially above those reported for Superfund Sites in the USA (e.g. Garrison et al 2014;Taylor et al 2019).…”

“…The existence of DDT and metabolites in the investigation area can be explained by the highly reducing environmental conditions (Taylor et al 2019), for which e.g. a half-life time of up to 65 years has been calculated (Clow et al 2017).…”

“…Hence, this is an important effect in particular for the risk assessment of pollutants. The underlying physical and chemical processes or phenomena potentially responsible for this apparent sequestration of persistent, bioaccumulative and toxic substances (PBTs) by geo-sorbents are only partially understood (Nowak et al 2014;Kästner et al 2016;Schäffer et al 2018;Taylor et al 2019). Recent observations suggest that PBT interactions with geo-sorbents comprise different organic and inorganic surfaces and matrices, and distinctions are clearly visible along these lines particularly with regard to the roles of inorganic micropores (e.g.…”

“…Pesticides such as DDT, exhibiting the main contamination revealed in this study, are well-known pollutants. They are characterized by high enrichment factors in sediment (Eganhouse and Pontolillo, 2008;Eganhouse et al 2018, Taylor et al 2019, resulting in a strong tendency for geo-accumulation, act as sinks and long-term sources for aromatic organic halogens (AOHs).…”

Legacy and Current‐Use Contaminants in Sediments Alter Macroinvertebrate Communities in Southeastern US Streams

“…Pesticides from urban sources that accumulate in freshwater stream sediments are recognized stressors (Nowell et al 1999) that have received less attention than other groups of pollutants (Nowell et al 1999, 2016) or other types of instream stressors, such as habitat, nutrients, and contaminants in water (US Environmental Protection Agency 2004). Contaminants in sediments are often investigated specifically in terms of a given source or location or a single contaminant or contaminant class, such as pyrethroids (Amweg et al 2006), polycyclic aromatic hydrocarbons (PAHs; Cox and Clements 2013), trace elements (hereafter termed metals; Canfield et al 1994; Besser et al 2015a), legacy organochlorine pesticides (OCPs), total polychlorinated biphenyls (TPCBs) and/or polychlorinated dibenzo‐p‐dioxins and dibenzofurans (Khim and Hong 2014; Rasmussen et al 2015; Taylor et al 2019). A few studies have monitored current‐use pesticides (CUPs), including pyrethroids, in bed sediment on a broad geographic scale (e.g., Hladik and Kuivila 2012; Moran et al 2017; Wei et al 2017).…”