Field and laboratory evaluation of the influence of copper‐diquat on apple snails in Southern Florida

Abstract

The recent decline of apple snail (Pomacea paludosa) populations in canals surrounding Loxahatchee National Wildlife Refuge in southern Florida coincided with the use of copper‐diquat for the control of the aquatic weed hydrilla (Hydrilla verticillata). Field and laboratory studies were designed to assess the effects of copper‐diquat on apple snails, which are the primary food of the endangered snail kite Rostrhamus sociabilis (formerly known as the Everglade kite). Acute toxicities (96‐h LC50 values) of Cutrine‐Plus and Komeen (chelated formulations of copper) to immature apple snails were 22 and 24 μg/L, respectively. Diquat was toxic at a concentration of 1,800 μg/L and did not increase the toxicity of copper when the chemicals were used in combination. Evaluation of field samples indicated that copper concentrations were higher in detritus than in water, plants and mud, and that there was a gradient of copper concentration from the canal to the interior, the highest residues being in samples from the canal. Copper associated with detritus (up to 150 μg/g) had no effect on growth or survival of apple snails in field cage and tank studies. Also, field applications of copper‐diquat to hydrilla had no effect on survival of caged adult and immature snails. Copper from field applications was rapidly taken out of solution by plants and organic material in the water and subsequently incorporated into the bottom detritus. Although the effects of repeated applications of copper‐diquat and high body burdens of copper (accumulated during exposure to herbicidal treatment) on survival and reproduction of apple snails are not known, the information available indicates that treatment of hydrilla with copper‐diquat was probably not responsible for the decline in the apple snail population. Application at recommended rates should pose no threat to these snails in the organically rich waters of southern Florida.

Effects of Copper, Nickel and Zinc on Three Species of Oregon Freshwater Snails

“…However, the operculate snails in our study had low copper LC50 values (0.015 and 0.008 mg/L). Pomacea paludosa, an operculate snail found in Florida and Georgia, was found to be relatively sensitive to copper, with a 96-h LC50 of 0.023 mg/L [15].…”

Effects of Aquatic Herbicides and Housing Density on Abundance of Pond-Breeding Frogs

“…However, Cutrine®-Plus and diquat have been noted to have a synergistic toxicity on a number of fish species including brown trout (Simonin andSkea, 1977 andDaniel, 1967). However, Cutrine®-Plus or Komeen® combined with diquat is not synergistic against apple snail (Winger et al 1984). Diquat and parathion act in a synergistic manner against the mosquito fish (Shearer and Halter, 1980) and diquat plus the fungicide nabam behave in a synergistic manner against embryos and tadpoles of Rana pipiens.…”

Remedial Investigation Report on Chestnut Ridge Operable Unit 2 (Filled Coal Ash Pond/Upper McCoy Branch) at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee. Volume 1. Main Text

“…Snails respond behaviorally to differences in water quality. When toxicants are present, for example, they may cease feeding, slough their tentacles or retract their foot, or actively attempt to avoid the conditions by moving downstream or crawling out of the water (Burris et al 1990 Winger et al 1984, Burris 1987. These findings suggest that quantifiable changes in snail activities could be used to describe water quality.…”