Environ. Sci. Technol. 2010, 44, 8541–8546
Occurrence and Relationship of Organophosphorus Insecticides and Their Degradation Products in the Atmosphere in Western Canada Agricultural Regions RENATA RAINA,* PATRICIA HALL, AND LINA SUN Department of Chemistry and Biochemistry, and Trace Analysis Facility, University of Regina, Regina, Saskatchewan S4S 0A2, Canada
Received July 19, 2010. Revised manuscript received September 11, 2010. Accepted October 11, 2010.
This paper presents the atmospheric occurrence and seasonal variations of the most frequently detected organophosphorus insecticides (OPs) and their OP oxon degradation products at Bratt’s Lake, Saskatchewan in the Canadian Prairies (April 2003 to March 2004, January-December, 2005) and at Abbotsford in the Lower Frazer Valley (LFV) of British Columbia from May 2004 to December, 2005. During 2005 there were 10 OPs, 8 OP oxons, and 6 other OP degradation products measured. The most frequently detected OPs were chlorpyrifos, malathion, and diazinon. At Bratt’s Lake the highest atmospheric concentrations were observed for chlorpyrifos, with maximum concentrations observed during July and August in 2003 showing much higher concentrations than those from 2005. This was related to its usage for grasshopper control in the province. At Abbotsford, diazinon and malathion were observed in much higher atmospheric concentrations than chlorpyrifos. Concentrations reached maximum in spring for diazinon and summer for malathion. This study is the first reported study of seasonal variations of OP oxons with their parent OP. Chlorpyrifos oxon concentrations during July were generally low, indicating strong local source contributions. The chlorpyrifos oxon/chlorpyrifos ratio and diazinon oxon/diazinon ratio showed a strong seasonal variation with increasing ratio from spring to summer which was attributed to increasing sunlight hours. Malathion oxon/mathion at both sites was similar and relatively constant throughout the year. The oxon/thion ratio represents a good indicator of age of source or contributions from local versus regional atmospheric sources.
Introduction Organophosphorus insecticides (OPs) have been used in agricultural areas to protect crops from pests such as grasshoppers, aphids, crown borers, fruit worm larvae, weevils, wheat midge, cutworms, and bertha armyworms. OPs can be applied throughout the growing season or more sporadically during infestations. In this study we investigate two distinct agricultural regions in western Canada that include the following: the prairies where grain and oil seeds such as wheat, barley, oats, canola, and flax are dominant * Corresponding author phone: (306) 585-4012; fax: (306) 3372409; e-mail:
[email protected]. 10.1021/es102450k
2010 American Chemical Society
Published on Web 10/26/2010
and OP applications are expected to be applied more sporadicly for grasshopper control (1); the Lower Fraser Valley (LFV) in British Columbia (BC) where fruit and berry production dominates and usage of OPs is recommended throughout a longer period of the growing season (2). The 2003 provincial usage inventories show that in 2003 the primary OPs used for agriculture in British Columbia were diazinon and malathion (3), while in Saskatchewan the primary OP was chlorpyrifos (4). Chlorpyrifos, malathion, or diazinon have also been detected in runoff water or atmospheric samples in a number of urban settings in North America (5-7) and have a variety of domestic uses including termite control, landscaping applications, and home ornamental gardens (5-9). The most recent year for pesticide usage (agricultural) information is for 2003 for Canada (3, 4), and 2002 for the United States which is available through the USGS National Pesticide Synthesis Project (10). Our previous studies provided the first detection of OP degradation products in atmospheric samples in Canadian agricultural regions (13) and from selected samples confirm the dominance of specific OPs in each of the regions as expected from 2003 usage inventories (11-13). Within Canada selected OPs have also been monitored by Environment Canada in short-term air sampling campaigns of currently used pesticides during 2004 and 2005 in which 10 different OPs were detected (14), and in the LFV, malathion and chlorpyrifos were also detected in studies during 2003 (15). An earlier study (between 1994 and 1996) in a small watershed in the Canadian prairies (Manitoba) detected the presence of high concentrations of chlorpyrifos in precipitation and air late in the summer (16). In the United States a number of studies in agricultural areas also investigated the presence of selected OP in fog samples (17-19) or atmospheric samples (20-23). OPs are of concern due to their toxicity (24-29), and OP oxon degradation products have greater toxicity than their parent thions. Chlorpyrifos oxon and malathion oxon are approximately 100 times more toxic than their parent thion, while diazinon oxon is approximately 10 times more toxic than diazinon (28). The United States Environmental Protection Agency (USEPA) and manufacturers of OPs in the US reached an agreement that cut diazinon and chlorpyrifos in urban settings through a mandated 25% decrease in production in 2002 and 50% decrease in 2003 in the United States (30). OPs however are still used in Canadian urban environments as well as in agriculture in North America. OP degradation reactions in the environment include photochemical oxidation, in air or on vegetation, and hydrolysis, which is more important in soil, water, and sediment (31-33). The oxidative desulfuration process involves the conversion of the PdS bond to PdO forming OP oxons (19). In addition to our first detection of OP oxons in air samples at Canadian agricultural regions (13), several other selected studies in other countries have detected selected OP oxons in water (34), fog (19), and frogs (28). Few studies have investigated occurrence of OP degradation products in the atmosphere, their relationship to the active OP ingredient applied, and the proximity to application region. In addition, seasonal and annual variations of OPs and their degradation products in the atmosphere have not been studied.
Methods Site Description and Air Sampling at Bratt’s Lake, Saskatchewan (SK). The Environmental Canada sampling site at Bratt’s Lake, SK (latitude 50°12′10′′N, longitude 104°12′ 15′′W) is a field site in the prairie agricultural region located VOL. 44, NO. 22, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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within the dark brown soil zone. Environment Canada conducts other monitoring at this site through CAPMoN (Canadian Air and Precipitation Network) and BSRN (Baseline Surface Radiation Network). Air samples analyzed for OP pesticides were collected during April 2, 2003 to March 5, 2004 and January 1, 2005 through December 31, 2005. Highvolume air samplers (Model PS-1, Tisch) were operated continuously at a flow rate of 225 L/min such that air volume was ∼3600 m3 for 7-day samples. In 2005, 7-day samples were collected using a mixture of 7 g of XAD-2 and 7 g of Tenax-TA as the sorbent. During the ∼1 year period starting April 2003, the effectiveness of the solid sorbent used for gas-phase collection of OCs and OPs was evaluated and showed that all seven sorbents tested were in general more effective than a standard 7.6 cm PUF with XAD-2, XAD-4, and Tenax TA among the most effective solid sorbents (35). In 2003, air samples were collected for either 1 day, 2 days, 4 days, or 7 days with shorter sampling periods selected during the agricultural growing season (see Supporting Information). The data presented herein for OPs are obtained from a PS-1 sampler with a sampling module containing PUF/sorbent except for a few selected periods where the pesticide concentrations obtained from a colocated PS-1 sampler containing a sampling module with only a 7.6 cm PUF were higher than those obtained from PUF/Chromosorb 750, as this sorbent was shown to have significant breakthrough for some sample collection periods (35). All 2005 samples were analyzed for OP degradation products, while for 2003 samples sufficient extract was only available for 12 samples and include most of the sampling periods with high levels of chlorpyrifos. OP degradation products included OP oxons, 2-isopropyl-6-methyl-4-pyrimidinol (IMP), 3,5,6-trichloro2-pyridinol (TCP), and diethyl phosphate (DEP), isomalathion, malathion monocarboxylic acid and O-methoate (see Table S1 and S2, Supporting Information, for recoveries and method detection limits). All sampling modules were prepared in a class 1000 cleanroom laboratory (particle count limit of 1000 particles 0.5 µm or larger per cubic foot of air) at the University of Regina. Fifty nine field and shipment blanks were collected in Bratt’s Lake during this study with no detected levels of pesticides observed. Site Description and Air Sampling for Abbotsford, British Columbia (BC). The Agriculture Canada/Environment Canada/Greater Vancouver Regional District (GVRD) (AQ Station T034) field station, located in Abbotsford, is in the middle of the Lower Fraser Valley (LFV). It is located in Region 2 (Lower Mainland) of the province of BC. From May 5, 2004 to the end of December, 2005, 7-day samples were collected using a high volume PS-1 sampler in order to assess the seasonal variation of OPs and other fungicide levels in the LFV (12, 36). The 2005 sample extracts were also analyzed for OP degradation products. Air sampling heads with the filter and PUF/7 g XAD-2/7 g Tenax-TA combination were prepared in a class 1000 cleanroom laboratory at the University of Regina and shipped to Environment Canada staff in BC (preloaded). The seven field blanks showed no detectable levels of pesticides. Sample Analysis. The sample extraction, cleanup, and instrumental analyses methods have been described previously (11-13, 35) and more detail is provided in Supporting Information. GC/MS was used for analysis of OPs for 2003 extracts from Bratts Lake (see Table S2, Supporting Information, for list) and for chlorpyrifos, malathion, and diazinon from 2004 extracts. LC/MS/MS analysis was used for analysis of all degradation products and OPs for 2005 samples from both sampling locations. Calibration range for sample analysis is MDL-100 ng mL-1, and higher concentration sample extracts were diluted into calibration range using isotope dilution. Typical range of dilution factors were 0.5 8542
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to 0.04 (12). Diazinon-d10 was used as the internal standard at 100 ng mL-1 for GC/MS and 10 ng mL-1 for LC/MS/MS. Total Suspended Particulate Concentrations. The filters used in the PS-1 sampling module were weighed ((1.5 µg) before and after sampling using a Mettler Toledo microbalance housed in a glovebox with a UHP nitrogen atmosphere for humidity control. Filters were conditioned in the glovebox for a minimum of one day prior to gravimetric analysis. The total suspended particulate (TSP) concentration was determined by dividing the particle mass collected on the filter by the total air volume sampled.
Results and Discussion Weather Conditions, TSP Levels, and Pesticide Usage Information. In 2003 at Bratt’s Lake, SK, the precipitation amounts were much lower than subsequent years, and this is also apparent in higher TSP levels during 2003 as compared to 2004 and 2005 (Figure S1, Supporting Information). The dry conditions along with slightly higher temperatures (above 30 °C) during the summer of 2003 as compared to 2005 also coincided with a higher forecast density of grasshoppers in southern regions of Saskatchewan including the region around the Bratt’s Lake sampling site in 2003 (37). The grasshopper forecast maps are based on observations of adult grasshopper populations made from the previous fall populations. The forecasts were consistent with observations of a large increase in grasshopper population at Bratt’s Lake during 2003. Chlorpyrifos is used predominately for grasshopper eradication in Saskatchewan with 2003 sales of 205562 kg of which 45 and 55% were used in the dark brown and dark gray soil zones in 2003 (4). Bratt’s Lake is located in the dark brown soil zone region of Saskatchewan with the brown and dark gray soil zones in closest proximity (38). The 2003 chlorpyrifos usage is much greater than in previous years when usage was 7267 kg (69% dark brown soil zone) and 121824 kg (99.8% in dark brown soil zone) in 2001 and 2002, respectively. All reported Saskatchewan usage of chlorpyrifos is in these two soil zones of the province, but significant annual shifts in location of application exist due to changes in regions of grasshopper infestations. Malathion is also used with 58% and 42% of the total 1327 kg used in the dark brown and brown soil regions of Saskatchewan, and provincial usage has remained around 1000 kg throughout 2001-2003 (4). Malathion usage is further north and to the east and west of Bratt’s Lake where is it expected to be primarily applied to Saskatoon berries. In the states south of Saskatchewan, 2002 usage is low (10) and is expected to be a minor contributor. Our tests of selected samples with high chlorpyrifos concentrations in the gas phase showed below MDL in the particle phase. Our previous studies on several fungicides in the LFV of BC have shown that at Abbotsford, TSP levels during 2004-2005 are much lower than those at Bratt’s Lake and range between 10-40 µg m-3 with generally lowest total suspended particulate levels during the winter months (36). Climatic conditions were relatively similar between the summers of 2004 and 2005. Fungicides such as captafol were shown to have a significant particle-phase fraction which was related to inverse temperature and shows the importance of short versus long-range atmospheric transport (36). All samples were analyzed for particle-phase OPs (diazinon, malathion, and chlorpyrifos) and showed only small contributions (
