Environ. Sci. Technol. 1996, 30, 845-851
Fate and Atmospheric Concentrations of r- and γ-Hexachlorocyclohexane in Que´ bec, Canada LAURIER POISSANT* AND J E A N - F R A N C¸ O I S K O P R I V N J A K Atmospheric Environment Directorate, Environment Canada, 100 Boulevard Alexis-Nihon, Saint-Laurent, Que´bec, Canada H4M 2N8
The atmospheric concentration of lindane and R-HCH measured at Villeroy (Que´ bec, Canada) are presented. Time-series and source-receptor recognition techniques permit us to point out that agricultural activities, namely, corn seeding, are mainly responsible for the atmospheric release of lindane. About 350 000 ha of land are used for this crop activity in Que´ bec, and the period of seeding appears to be concomitant with the highest peak of atmospheric lindane. The relationship of lindane with temperature shows that desorption mechanisms are important processes in the atmospheric lindane buildup. This volatilization might come from soil and might involve old as well as fresh lindane.
annual production and use of HCH amounts to 200 000 t (8), and the global production of lindane amounted to 5000 t in 1984 (5). In Canada, recent lindane imports of 100150 t/year are reported (3). In the free environment, Rand γ-HCH have specific lifetimes. The hydroxyl radical reaction rate constants in air for both are estimated to be 6.9 × 10-12 cm3 molecule-1 s-1 (9, 10). The reaction rate constant combined with concentrations of 4 × 105 hydroxyl radicals/cm3 (24-h average) leads to a photooxidation lifetime of about 4 days. It seems that the hydroxyl radical is the primary mechanism influencing the lifetime (11). There is no known data on the photolysis lifetime (10). However, lindane has been reported in some literature to be photochemically active in the environment. Malaiyandi and Shah (12) have reported that when exposed to sunlight in a quartz flask, lindane (94% pure) converted to R-HCH, resulting in a 31% increase of the latter after 38 h of exposure to sunlight. Other literature has recognized R-HCH as a byproduct of the decomposition of lindane (13-16), whereas some other literature found no evidence that lindane is isomerized to R-HCH (8) but rather is rapidly degraded through dechlorination to form pentachlorocyclohexenes (PCCH) and tetrachlorocychlohexene (TCCH) (5). The chemical pathway leading to the elimination of lindane in the environment appears to involve dechlorination and/or translocation. The purpose of this paper is to study, through the annual time-series of lindane and R-HCH, their source-receptor relationship and their behavior as related to the ambient temperature and, to a certain extent, to figure out their potential atmospheric chemical fate in Que´bec (Canada).
Methods Introduction Pesticides have been extensively used since the 1950s and have been distributed worldwide. Some of them have relatively high volatilities, causing them to evaporate quickly after application and be dispersed through the atmosphere (1). As a consequence, they are spread out and omnipresent in the environment even in remote areas (2-4). Organochlorine pesticides, the most persistent pesticides in the free environment, are used as broad-spectrum insecticides for treatment of seeds and soil, application on trees, timber, and stored materials as well as for treatment of animals against ectoparasites and for public health (antimalarial) (5). HCH, named to describe the mixture of nine stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane [seven meso forms and one pair of enantiomers (optical isomers)], is one the most important organochlorine pesticides found in the environment (5). There are two formulations of HCH on the international market: pure lindane (γ-HCH 99%), which is one of the top 10 insecticides used in Canada (6); and the HCH technical grade, which is an isomeric mixture in the proportions 55-80% R, 5-14%, γ, 2-16% δ, and 3-5% -HCH (although all isomers are toxic, only lindane is insecticidal). The latter formulation has been banned in Canada and the United States since the 1970s, but is still used in some countries. Cumulative world production of HCH has likely reached several million tons (7). Total global * Corresponding author e-mail address:
[email protected].
0013-936X/96/0930-0845$12.00/0
1996 American Chemical Society
Sampling Site and Technique. The station at Villeroy is located in a rural setting along the St. Lawrence River between Trois-Rivie`res and Que´bec City at 46°26′ N latitude and 71°56′ W longitude. The site is a grassy rural area surrounded by farms and some wooded areas. The area is about 50 km north of the Que´bec corn crop belt. The monitoring instruments were installed on a platform (10 m × 10 m), which stood 1 m aboveground. Samples were collected by pulling 280-400 m3 of air through a glass fiber filter, which trapped particles, followed by a polyurethane foam (PUF) plug [6 cm in diameter by 8 cm long, density ) 0.022 g/cm3 (weight ) 4.98 g)], which collected vaporphase compounds. The sampling frequency was every sixth day for 24 h. Prior to sampling, the filter and PUF were cleaned to remove any adsorbed organic material. This was done by a 12-h Soxhlet extraction using acetone (10 cycles/h) followed by dichloromethane also for 12 h. The filter and PUF were then put onto separate pieces of prerinsed (with GC/MS quality acetone) aluminum foil in a drying oven for 12 h. Once dry, the filter and PUF were wrapped in their aluminum foil and sealed in separate plastic bags. Both bags were then sealed in a third bag. At the sampling site, the filter was installed on a metal grill filter-holder, and the PUF was installed in an acetone-rinsed glass cylinder, which once installed in a metal casing screws onto the bottom of the filter holder. All manipulations with the filter and PUF were done using plastic gloves and acetone-rinsed aluminum tweezers. The filter-PUF holder was then taken outdoors and installed in the sampler.
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TABLE 1
Summary of r-HCH and γ-HCH Concentrations in Vapor Phase at Villeroy (PQ) in 1992 compd (pg/m3)
γ-HCH R-HCH (pg/m3) ratio (γ/R) ratio (R/γ)
sample size
arithmetic mean
geometric mean
median
min
max
CV (%)
58 56 56 56
37.2 31.6 1.3 4.8
14.8 26.2 0.6 1.8
17.5 36.2 0.7 1.4
