Combining coring and suction cup data to improve the monitoring of pesticides in sandy vadose zones: a field-release experiment

Soil coring and vertically and horizontally installed suction cup monitorin g techniques were compared during a field release experiment conducted in a n urban area of the Swan Coastal Plain of Western Australia. Sodium bromide and low concentrations of diazinon, chlorpyrifos, atrazine and fenamiphos were released into the vadose zone and rater of migration and mass loss wit h respect to a bromide tracer investigated. Only bromide and atrazine showe d significant migration through the vadose zone. The relative hall-life mas s losses from the vadose zone of the pesticides ranged from 3 to > 40 days. The use of soil coring complemented the use of vertically and horizontally installed suction cups For investigating relatively mobile non-volatile com pounds, such as atrazine. Data from horizontally installed suction cups acc ounted for mass losses due to dilution and transport that could not be acco unted for by coring, and enabled a better estimate of degradation and migra tion rates through the vadose tune. From core data alone, atrazine migratio n rates for the first 0.25 m were underestimated by more than 50% (0.0039 i n day(-1) compared to 0.013 m day(-1)), and removal rates (and inferred deg radation rates) were overestimated by more than 100% (half-lift: of 14 days compared to a half-life of 40 days), compared with rates determined by usi ng core data and horizontal suction cup data in combination. Migration rate s may have been even further underestimated at greater depths. (C) 2000 Els evier Science B.V. All rights reserved.