A dynamic mass budget for toxaphene in North America

Abstract

A continental-scale dynamic mass budget for toxaphene in North America is presented, based on available information on physicochemical properties, usage patterns, and reported environmental concentrations and using the Berkeley-Trent North American mass balance contaminant fate model (BETR North America). The model describes contaminant fate in 24 ecological regions of North America, including advective transport between regions in the atmosphere, freshwater, and near-shore coastal water. The dynamic mass budget accounts for environmental partitioning, transport, and degradation of the estimated 534 million kg of toxaphene that were used in North America as an insecticide and piscicide between 1945 and 2000. Satisfactory agreement exists between model results and current and historically reported concentrations of toxaphene in air, water, soil, and sediments throughout North America. An estimated 15 million kg of toxaphene are believed to remain in active circulation in the North American environment in the year 2000, with the majority in soils in the southern United States and Mexico, where historic usage was highest. Approximately 70% of total toxaphene deposition from the atmosphere to the Great Lakes is attributed to sources outside the Great Lakes Basin, and an estimated total of 3.9 million kg of toxaphene have been transported to this region from other parts of the continent. The toxaphene mass budget presented here is believed to be the first reported continental-scale multimedia mass budget for any contaminant.

Soil-air relationships for toxaphene in the southern United States

“…Previous models of toxaphene emission from soils, atmospheric transport, and deposition have considered only the whole technical mixture [16][17][18][19][20][21]. MacLeod et al [21] concluded that ''a major refinement would be to model the toxaphene mixture as individual homolog groups rather than as a single chemical compound.'' This work provides a basis for modeling the fractionation that takes place when toxaphene evaporates from soils.…”

“…An early transport model predicted dispersal of toxaphene from usage areas in the southern United States and deposition into the Great Lakes [20]. More recently, MacLeod et al [21] applied the Berkeley-Trent North American mass balance contaminant fate model (BETR North America) to modeling the dynamic mass budget for toxaphene between 1945 to 2000 [21]. Of the 5.34 ϫ 10 5 t of toxaphene that were used in North America, it was estimated that 1.5 ϫ 10 4 t (3%) remained in active circulation as of the year 2000; 6.5 ϫ 10 4 t (12%) had been removed from the continental environment by advection of air and water and burial in soils and sediments; and 4.54 ϫ 10 5 t (85%) had been removed by degradation reactions.…”

“…As one of the 12 persistent organic pollutants targeted for , toxaphene applications are expected to cease. Because toxaphene usage in North America has been discontinued almost entirely, emissions from soils and water will control the overall level of continental contamination in the future [21]. MacLeod et al [21] noted that significant impediments to creating the BETR North America model for toxaphene were lack of knowledge about emissions, environmental fate and transport processes, degradation rates, and physicochemical properties.…”

“…Because toxaphene usage in North America has been discontinued almost entirely, emissions from soils and water will control the overall level of continental contamination in the future [21]. MacLeod et al [21] noted that significant impediments to creating the BETR North America model for toxaphene were lack of knowledge about emissions, environmental fate and transport processes, degradation rates, and physicochemical properties. In 1999 and 2000, we sampled soil and overlying air at farms in the southern United States to investigate soil-to-air exchange of organochlorine pesticides, including toxaphene.…”

Modeling of temporal patterns and sources of atmospherically transported and deposited pesticides in ecosystems of concern: A case study of toxaphene in the Great Lakes

“…[48] The migration of toxaphene in North America was studied using different approaches including back trajectory [James and Hites, 2002], mass balance [MacLeod et al, 2002], and regional scale dispersion [Ma et al, 2005] models. However, the previous studies have not investigated the relative importance of the Mexican soil residues, U.S. soil residues, and global background on the depositions into the individual Great Lakes.…”