Environmental fate and ecological impact of copper hydroxide: Use of management practices to reduce the transport of copper hydroxide in runoff from vegetable production

Abstract

Vegetable production practices combining copper-based pesticides with polyethylene mulch create conditions for highly toxic runoff emissions to surface waters. Copper hydroxide is a widely used fungicide-bactericide approved for both organic and conventional agricultural production of vegetable crops for control of diseases. Copper-based pesticides are often viewed as more "natural" than synthetic organic pesticides, but aquatic biota, such as the saltwater bivalve Mercenaria mercenaria, are extremely sensitive to low concentrations of copper. The use of polyethylene mulch in organic and traditional vegetable production is gaining popularity because it decreases pesticide use and warms the soil allowing for earlier crop planting, but its use also increases runoff volume and soil erosion. Two field studies were conducted to evaluate the effectiveness of management practices to reduce loads of copper in runoff from tomato production. Seasonal runoff losses of 20 to 36% of applied copper hydroxide were observed in tomato plots using plastic mulch with bare soil furrows. The addition of vegetative furrows between the raised, polyethylene-covered beds or the replacement of polyethylene mulch with vegetative residue mulch reduced copper loads in runoff by an average of 72 and 88%, respectively, while maintaining harvest yields. Use of these alternative management practices could reduce surface water concentrations in nearby streams from the observed 22 μg/L to approximately 6 and 3 μg/L, respectively, which would be below the median lethal concentration for larval clams (M. mercenaria 96-h LC 50 = 21 μg/L) and close to or below the EPA guidelines to protect aquatic life (24-h average = 5.4 μg /L for fresh water and 4.0 μg /L for salt water).