Inputs of copper-based crop protectants to coastal creeks from pasticulture runoff

Inputs of copper-based crop protectants from tomato fields grown under plastic mulch agriculture (plasticulture) to an estuarine creek were investigated. Copper was measured in runoff from diverse land-uses including conventional agriculture, plasticulture, residences, and natural areas. Water column and sediment copper concentrations were measured in plasticulture and control (nonagriculture) watersheds. Copper concentrations in plasticulture-impacted creeks exceeded background levels episodically. High concentrations occurred during or immediately after runoff producing rains. Concentrations of 263 mug/L total copper and 126 mug/L dissolved copper were measured in a tidal creek affected by plasticulture; concentrations exceeded the shellfish LC50 values and the water quality criteria of 2.9 mug/L dissolved copper. Control watersheds indicated background water column levels of less than or equal to 4 mug/L dissolved copper with similar copper levels during periods with and without rain. The copper concentrations in tomato plasticulture field runoff itself contained up to 238 mug/L dissolved copper. Copper concentrations in runoff from other land-uses were less than 5 mug/L dissolved copper. Creek sediment samples adjacent to a plasticulture field contained significantly higher copper concentrations than sediments taken from nonplasticulture watersheds.