ABSTRACT

 Land snails (Achatina achatina) are readily consumed in Southeastern Nigeria, and they are often collected from the wild including cocoa plantations which are commonly sprayed with copper-based fungicides to combat the cocoa black-pod disease. This study was conducted to assess the possible accumulation of heavy metals (Cu, Cd, Pb, Fe, and Mn) in land snail species (Achatina achatina), soil, leaf litters and selected plants obtained from Ajata and Itunta cocoa plantations located in Bende and Ikwuano Local Government Areas, of Abia State respectively. Snail samples were collected during the rainy and dry seasons, in a two-by-three factorial design while the other samples were collected in a single-factor randomized complete block design. The snails were weighed and categorized into three sizes juvenile, medium and large and then dissected into three morphological parts, edible part (muscle), non-edible (intestine) and shell. The metal contents of the samples were determined using the Atomic Absorption Spectrophotometer, after acid digestion. The results showed that heavy metal concentrations in snail samples harvested from the cocoa plantations were higher than in those from the control site. The mean concentrations of the metals in the soil, leaves litter and the snails varied significantly (p≤0.05) in all locations in both seasons; with Ajata having the highest mean Cu concentrations. Pb contents of the various samples were generally below the detectable limits of the equipment used. Mean metal concentrations of the different snail sizes did not vary significantly (p≥0.05), whereas highly significant differences (p≤0.05) occurred in the mean Cu, Cd and Fe concentrations of the morphological parts examined. Cu and Cd concentrations in snail parts had the trend of intestine > muscle > shell; but Fe concentration had a different pattern: shell > intestine > muscle. Cu ranged from 0.72mg/kg in the shell to 54.68 mg/kg in the intestine, Cd varied from below detection level in the shell to 18.88 mg/kg in the intestine, while Fe ranged from 10.05 mg in the intestines to 200.66 mg/kg in the shells. Results on possible uptake and accumulation of the metals in snails tissues showed bio-accumulation factors (BAF) < 1 for all the metals in the muscles of the snails whereas the intestine contained metals with BAF>1, showing that the metals ingested from the soils or feed materials are mainly accumulated in the intestinal parts of the snail. The mean metal levels in the studied samples were mostly higher in the dry season. Nevertheless, the mean concentrations of the metals in the edible snail parts (muscle) across all sizes were lower than their permissible FAO/WHO levels. The hazard quotient (HQ) values for adults and children for all the metals analyzed were less than 1. The results also revealed that the estimated intakes for all ages and consumption amounts were lower than the Provisional Tolerable Dietary Intake (PTDI) values for all metals except Cd. Thus, consumption of snails obtained from the cocoa plantations investigated does not pose any significant toxicity risk to consumers. However, routine assessments of wild food especially snails collected from plantations where Cu-based fungicides is highly recommended. This will alert the public of possible heavy metal pollution concerns.