1628 Environmental Toxicology and Chemistry, Vol. 21, No. 8, pp. 1628–1637, 2002  2002 SETAC Printed in the USA 0730-7268/02 $9.00 + .00 A DYNAMIC MASS BUDGET FOR TOXAPHENE IN NORTH AMERICA MATTHEW MACLEOD,* DAVID WOODFINE,JENN BRIMACOMBE,LIISA TOOSE, and DON MACKAY Canadian Environmental Modelling Centre, Trent University, 1600 Westbank Drive, Peterborough, Ontario K9J 7B8, Canada ( Received 10 September 2001; Accepted 4 February 2002) 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. Keywords—Toxaphene Fate model Long-range transport Great Lakes INTRODUCTION Toxaphene is a complex mixture of chlorinated boranes produced by nonspecific chlorination of camphene. The Her- cules Company of Brunswick, Georgia, USA, first introduced it as an insecticide and herbicide in 1945 under the trade name Hercules 3965 [1,2]. Initially, toxaphene was applied primarily to cotton, but uses expanded to include other crop types and increased dramatically following the banning of DDT in the United States in 1972. A relatively small quantity of toxaphene was used as a piscicide to eradicate fish stocks perceived as undesirable [1,2]. Toxaphene is persistent in the environment and has a sig- nificant vapor pressure. Thus, it evaporates from sites of use and has become ubiquitous in the environment, detectable in trace amounts in air, water, sediments, and soils throughout North America and globally. Toxaphene contamination in the North American Great Lakes is an issue of particular public concern and scientific interest. Despite relatively small usage in the Great Lakes watershed, toxaphene is found in surpris- ingly high concentrations particularly in Lake Superior, which is remote from areas where usage occurred. Toxaphene con- tamination has impacted the Great Lakes ecosystem. For ex- ample, 69% of fish consumption restrictions recommended by the Ontario, Canada, government for Lake Superior are due to toxaphene [3]. It is widely believed that the contamination of Lake Superior is due to atmospheric deposition of toxa- phene, with transport from cotton-growing regions in the southern United States playing a significant role. Chemical fate and transport models have contributed sig- nificantly to understanding the transport of toxaphene to the Great Lakes and its fate in the aquatic ecosystem. For example, Rice et al. [4] and Voldner and Schroeder [5] estimated tox- * To whom correspondence may be addressed (mmacleod@trentu.ca). aphene deposition rates to the Great Lakes using atmospheric trajectory models. Swackhamer et al. [6] used an air–water– sediment interaction model to explain concentration differ- ences between the Lakes and modeled the transfer of toxaphene between the lakes and the atmosphere. Models based on the mass balance principle offer the added advantage of accounting for the ultimate fate and transport of every kilogram of chem- ical released to the environment. These dynamic mass budgets for individual chemicals, when verified against experimental data, establish a quantitative understanding of sources, trans- port, and removal processes. A model capable of producing verifiable mass budgets provides a sound framework for for- mulating responsible chemical management strategies for other chemicals. Unfortunately, a lack of knowledge about emission rates, environmental fate and transport processes, chemical degradation rates, and even physicochemical properties of the chemical itself create significant impediments to compiling dynamic mass budgets describing environmental fate. Few ex- amples have been reported. The objective here is to compile a dynamic mass budget for a persistent multimedia environmental contaminant on a continental scale, using toxaphene in North America as a case study and relying on a regionally segmented contaminant fate model, BETR North America [7]. The mass budget accounts for the fate and transport of all North American emissions of toxaphene that occurred between 1945 and 2000, tracking chemical migration between 24 ecological regions of the con- tinent. This comprehensive description of continental-scale fate and transport of toxaphene is presented in six stages: description of the BETR North America model, characteriza- tion of the properties of toxaphene, compilation of data on observed environmental concentrations, estimation of usage and emission patterns, steady-state modeling of fate and trans- port in North America, and dynamic modeling of toxaphene fate throughout its use history, with comparison between mod-