Problems and results of residue studies after application of molluscicides

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.

Section: Relation Of Copper To Apple Snail Population At Lnwrsupporting

confidence: 93%

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

Winger

Imlay

McMillan

et al. 1984

“…Other studies have demonstrated the photodegradation of TPT by ultraviolet light [23,27]. Strufe [28] showed that the ultraviolet irradiation of TPT acetate solutions in water resulted in the loss of 95% of the compound in 60 min. Ultraviolet treatment of TPT chloride in solution produced a series of degradation products, including inorganic tin, in 6 h [29].…”

Section: Discussionmentioning

confidence: 99%

Triphenyltin and its degradation products in foliage and soils from sprayed pecan orchards and in fish from adjacent ponds

Kannan¹,

Lee²

1996

Abstract-Triphenyltin (TPT) is a fungicide used on a variety of crops throughout the world. In this study, pecan orchards in central Georgia (USA) previously sprayed with commercial TPT hydroxide mixtures were found to have TPT concentrations of 8.5 to 37 g/g dry weight in foliage and 1.2 to 12 g/g dry weight in soil. Total phenyltin concentrations (monophenyltin [MPT] ϩ diphenyltin [DPT] ϩ TPT) in foliage and soils immediately after application were up to 72 and 26 g/g dry weight, respectively. Besides TPT, DPT and MPT were present in the leaves and soils, with MPT generally the predominant compound. The proportion of MPT to TPT in pecan leaves increased with time after spraying, which was indicative of photolytic degradation of TPT. Microbial degradation of radiolableled TPT in soil or sediment samples was slow, with only 5% degraded during a 14-d incubation period. Triphenyltin was absent from the subsurface soils (2 to 15 cm depth) even though it had been sprayed eight to 10 times a year at a rate of 850 g/ha for the past 10 years. In an orchard where the last spraying was carried out approx. 2 years ago, TPT was absent, but MPT was present at approximately the same concentration as recently sprayed orchards. Fish (blue gill, largemouth bass, and channel catfish) from a pond near a recently sprayed pecan orchard had TPT as well as DPT and MPT. The predominate phenyltin in all fish was MPT, with 22 g/g wet weight in the liver of catfish. Radiolabeled TPT was only slowly metabolized by the fathead minnow, with 2% of the TPT metabolized to DPT after 6 d of exposure via water. Photodegradation appears to be the major factor affecting the fate of TPT in soils.

“…However, in snails exposed to 1,000 μg/g of diM, consumption is not significantly reduced, whereas growth is. When considered alone, therefore, this mechanism is not sufficient to explain the reduction of growth in snails, even though high doses of diM could well act as a repellent, as reported by Strufe [25], for metal‐based molluskicides. In the groups with a food intake lower than that in the controls, appetite loss is also very likely due to the toxic effects of the contaminant.…”

Section: Discussionmentioning

confidence: 98%

The garden snail (Helix aspersa) as a bioindicator of organophosphorus exposure: Effects of dimethoate on survival, growth, and acetylcholinesterase activity

Cœurdassier

Saint-Denis²,

Vaufleury

et al. 2001

The garden snail (Helix aspersa) is currently used as bioindicator of metallic pollution. Our objective was to extend its use to organic chemicals by studying the effects and tissue concentrations of the organophosphorus pesticide dimethoate following dietary uptake. After exposure for four weeks to increasing doses of pesticide in the diet, the median lethal concentration (LC50) was determined to be 3,700 microg/g food. Clinical signs indicated a no-observed-effect concentration of 100 microg/g and a lowest-observed-effect concentration of 250 microg/g. The growth parameters were decreased with increasing exposure to the pesticide. The median effective concentration (EC50), which was evaluated based on both shell diameter and dry weight inhibitions, was 665 and 424 microg/g, respectively, and the EC10 was 180 and 145 microg/g, respectively. Accumulation in the viscera was related to the amount of dimethoate in the food. The bioconcentration factors were low (>6 x 10(-3)). Acetylcholinesterase (AChE) activity was strongly decreased (80% from 250 microg/g). In conclusion, we demonstrated that the species H. aspersa could be a useful sentinel organism for organophosphorus contamination surveys. Among the effects measured, the inhibition of AChE activities and clinical signs were the most sensitive, followed by the growth parameters. These results confirm the suitability of the garden snail for development of sublethal toxicity tests using primary consumers and aboveground organisms.