Long‐term fate and bioavailability of sediment‐associated polychlorinated dibenzo‐p‐dioxins in aquatic mesocosms

Abstract

The long‐term fate of four polychlorinated dibenzo‐p‐dioxin (PCDD) congeners in sediments and their bioavailability to benthic invertebrates were studied in littoral enclosures located in a small lake at the Experimental Lakes Area in northwestern Ontario. The PCDDs sorbed on sediment particles were added to the 5‐m‐diameter enclosures on June 12, 1985, and concentrations in sediment cores (0 to 6 cm) were determined over 1,800‐d (˜ 5 years). Concentrations of 1,3,6,8‐TCDD, 1,3,7,9‐TCDD, HpCDD, and OCDD in the sediment declined, with half‐lives of 4.4±1.7, 4.6±1.9, 6.2±3.1, and 6.0±2.8 year, respectively. Evaluation of the data for 1,3,6,8‐TCDD and OCDD using a sediment‐water exchange model suggested that the decline in PCDD concentrations was due to losses to the water column via diffusion of DOC‐associated PCDDs in pore water and via particle resuspension. After 5 years the PCDDs remained bioavailable to freshwater mussel (Anodonta grandis) and crayfish (Orconectes virilis) exposed to sediments for up to 78 d. The crayfish had higher mean biota‐sediment accumulation factors (BSAFs) for 1,3,6,8‐TCDD and 1,3,7,9‐TCDD (0.31–0.53) than did mussels (0.07–0.13), whereas BSAFs for HpCDD and OCDD in the two species were similar (0.03–0.09).

Historical decline and altered congener patterns of polychlorinated dibenzo‐p‐dioxins and dibenzofurans in fish and sediment in response to process changes at a pulp mill discharging into Jackfish Bay, Lake Superior

“…Polychlorinated dibenzo‐ p ‐dioxins and dibenzofurans (PCDD/Fs) are persistent organic pollutants that were historically formed as by‐products of elemental chlorine bleaching during pulp and paper production. They have received international attention because of their high toxicity and long half‐life in fish and sediment . The presence of PCDD/Fs has been linked to the bleaching process in pulp and paper production, particularly the historical use of molecular chlorine (Cl 2 ) as a bleaching agent .…”

Long‐term fate and bioavailability of sediment‐associated 2,3,7,8‐tetrachlorodibenzofuran in littoral enclosures

“…Segstro et al [12] also observed decreased concentrations of 1,3,6,8‐TCDD and octachlorodibenzodioxin in sediment of littoral enclosures after 5 years. They concluded that the decline was due to diffusion of DOC‐associated PCDDs out of the pore water (and via particle resuspension) to the water column.…”

“…They concluded that the decline was due to diffusion of DOC‐associated PCDDs out of the pore water (and via particle resuspension) to the water column. The walls of the enclosures used by Segstro et al [12] were cut off approximately 30 cm above the sediment, thereby allowing permanent removal of TCDD. The diffusive‐loss pathway would likely be less important in our study, because the walls of the enclosures were intact during the experiment, except briefly in 1991, when two of four treated enclosure walls were moved by shifting ice.…”

“…The initial elevated exposure may be related to the resuspension of sediment‐bound TCDF in the enclosures as a result of their replacement and repair after damage occurred in the spring ice melt. Sediment resuspension was also suggested as an explanation for high initial accumulation of 1,3,6,8‐TCDD in mussels in enclosures in ELA L304 [12]. Increased dissolved concentrations and particulate concentrations in the water column may have increased bioavailability for the organisms in the enclosures.…”

“…This may partially be a result of the low lipid found in crayfish (mean = 1.7%) as compared with other organisms, such as mussels, zooplankton, Hexagenia sp., and Chironomidae (means: 7.9, 25.8, 4.3, and 3.9%, respectively) and of the resulting conversion using the lipid ratio method for determining concentrations of TCDF in the lipid from wet weight analyses. However, crayfish also feed at a higher trophic level than the other organisms sampled, which has been suggested to be a factor that results in a higher accumulation of 1,3,6,8‐TCDD (compared with the rate of accumulation seen in mussels) [12].…”