A new sampler for collecting separate dry and wet atmospheric depositions of trace organic chemicals

Studies conducted in Saskatchewan and elsewhere have demonstrated the atmos pheric transport of agricultural pesticides and other organic contaminants and their deposition into aquatic ecosystems. To date these studies have fo cused on ambient concentrations in the atmosphere and in wet precipitation. To measure the dry deposition of organic chemicals, a new sampler was desi gned which uses a moving sheet of water to passively trap dry particles and gasses. The moving sheet of water drains into a reservoir and, during reci rculation through the sampler, is passed through an XAD-2 resin column whic h adsorbs the trapped organic contaminants. All surfaces which contact the process water are stainless steel or Teflon. Chemicals collected can be rel ated to airborne materials depositing into aquatic ecosystems. The sampler has received a United States patent (number 5,413,003 - 9 May 1996) with th e Canadian patent pending. XAD-2 resin adsorption efficiencies for 10 or 50 mu g fortifications of ten pesticides ranged from 76% for atrazine (2-chloro-4-ethylamino-6-isopropyl amino-S-triazine) to 110% for triallate [S-(2,3,3-trichloro-2-phenyl)bis( 1 -methyl-ethyl)carbamothioate], dicamba (2-methoxy-3,6-dichlorobenzoic acid) and toxaphene (chlorinated camphene mixture). Field testing using duplicat e samplers showed good reproducibility and amounts trapped were consistent with those from high volume and bulk pan samplers located on the same site. Average atmospheric dry deposition rates of three chemicals, collected for 5 weeks in May and June, were: dicamba, 69 ng m(-2) da(-1); 2,4-D (2,4-dic hlorophenoxyacetic acid), 276 ng m(-2) da(-1): and, gamma-HCH (gamma-1, 2, 3, 4, 5, 6-hexachlorocyclohexane), 327 ng m(-2) da(-1). (C) 1999 Elsevier S cience Ltd. All rights reserved.