The role of colloidal organic matter in the marine geochemistry of PCBs

Abstract

WITHDRAWN AD -sT~i~Bñ~c i~tZ4-2-ABSTRACT Polychlorinated biphenyls (PCBs) were used as model hydrophobic organic compounds (HOC) to study physical-chemical processes which affect the speciation and fate of HOC in coastal environments. The focus of this study is on the sorption of PCBs with colloidal organic matter in seawater, and the influence of this process on the distribution of PCBs in coastal sediments. Laboratory and field experiments were used to make quantitative estimates of PCB-organic matter sorption, and to test predictions of three-phase equilibrium models.A static headspace partitioning method was developed to measure the sorption of several individual chlorobiphenyls with colloidal organic matter enriched from coastal seawater by hollow fiber ultrafiltration. This technique directly measured the dissolved phase fugacity of PCBs in experimental bottles, and avoided uncertain separation techniques often used in isolating various chemical phases. Colloidal organic carbon normalized partition coefficients (Koc) were determined from linear sorption isotherms, and increased from 1.9 x 10' (L/Kg) for 2,4'-dichlorobiphenyl to 3.5 x 10 s for 2,2',3,4,5'-pentachlorobiphenyl. Sorption tended to increase with increasing octanol-water partition coefficients (Kow) of the sorbate, and values of Koc were within a range of those reported in other experimental sorption studies with sediments and dissolved humic substances. Experimental partitioning results support the hypothesis that HOC-organic colloid sorption is similar to HOC sorption by sediment organic matter.PCBs were measured in the interstitial waters and sediments of three box cores obtained from New Bedford Harbor and Buzzards Bay, Massachusetts. The three sites studied had a wide range of sediment PCB concentrations, and reducing conditions provided environments containing high concentrations of colloidal organic matter. Dissolved organic carbon (DOC) and total sediment organic carbon (TOC) were measured in two cores to test the role of organic matter on the observed partitioning of PCBs. PCB concentrations, particularly those of less soluble chlorobiphenyls, were highly elevated in interstitial waters compared to water column concentrations at all three sites. The measured apparent distribution coefficients (K'd) of individual chlorobiphenyls did not increase with hydrophobicity (Kow) and indicate that a large fraction of PCBs in interstitial waters must be sorbed to organic colloids. A three-phase equilibrium sorption model, in which dissolved PCBs are in a dynamic equilibrium with colloidal and sediment organic matter, accounts for many aspects of the field data. There is good agreement of observed partitioning at New Bedford Station 67 and Buzzards Bay Station M with model calculations based on predictions derived from laboratory experiments of HOC sorption with sediments and organic colloids, but model calculations underpredict K'd at Station 84 in New Bedford Harbor.-3-The sediment-interstitial water results were contrasted with a study of PCB pa...

Carbon cycling in coastal sediments: 1. A quantitative estimate of the remineralization of organic carbon in the sediments of Buzzards Bay, MA

“…Site M has been used for a variety of biogeochemical studies. It is the same location used by MARTIN and SAYLES (1987) for their study of transport rates in sediments and by BROWNAWELL (1986) as part of his study of PCBcolloidal organic matter interactions in pore water. Site M is the same as station 49 of Moore's bottom sediment study (MOORE, 1963), lie-s between stations K and L of Sanders' benthic community study (S~~~~Rs, 1958).…”

Biogeochemical Processes Governing Exposure and Uptake of Organic Pollutant Compounds in Aquatic Organisms

“…The partition parameters discussed in the preceding paragraphs, K and K, are based on the simplest partitioning process, two phases, and this works reasonably for many soil-water systems and sedimentwater systems. Three lines of evidence led Brownawell (32) and Brownawell and Farrington (43,44) to hypothesize that at least a three-phase partitioning model is needed to model the distributions of many hydrophobic compounds in interstitial waters of sediments: a) experimental evidence showing sorption of hydrophobic orpinic compounds to colloidal organic matter (45,46) (48,52,53). Field and laboratory evidence from several studies with PCBs has established that partitioning of hydrophobic compounds to colloids or very small particles must be considered in many natural water systems to account for the observed distributions of hydrophobic compounds in the dissolved and particulate fractions of water samples (43,44,54,55).…”

“…Field and laboratory evidence from several studies with PCBs has established that partitioning of hydrophobic compounds to colloids or very small particles must be considered in many natural water systems to account for the observed distributions of hydrophobic compounds in the dissolved and particulate fractions of water samples (43,44,54,55). Nomographs similar to those ofFigure 2 (32) have been presented (46,55,56) and are useful in providing first order assessments of the physical chemical state of a given hydrophobic pollutant in coastal, estuarine, riverine, lacustrine, and interstitial waters.…”

“…The association of a significant proportion of the interstitial water hydrophobic compounds such as the PCBs with a colloid fraction has important implications for the assessment ofthe flux of these compounds across the sediment-water interface (32). First-principle arguments indicate that hydrophobic compound interactions with colloids will also be important in modeling the environmental behavior ofcompounds that enter esuarine waters across a salinity and particulate matter gradient as material is carried down river, or in the case ofdischarge ofan industrial or municipal sewage effluent rich in organic matter content.…”

“…Nomograph for relationships between fraction (f,) of a given hydrophobic compound sorbed to organic colloids, organic colloid concentration, and log KOc of the compound. From Brownawell (32).…”