A field method using microcosms to evaluate transfer of Cd, Cu, Ni, Pb and Zn from sewage sludge amended forest soils to Helix aspersa snails.

Juvenile Helix aspersa snails exposed in field microcosms were used to assess the transfer of Cd, Cu, Ni, Pb and Zn from forest soils amended with liquid and composted sewage sludge. Zn concentrations and contents were significantly higher in snails exposed to liquid and composted sludge after 5 and 7 weeks of exposure, when compared with control. Trends were less clear for the other metals. Present results show that Zn, among the cocktail of metallic trace elements (MTE) coming from sewage sludge disposal, represents the principal concern for food chain transfer and secondary poisoning risks. The microcosm design used in this experiment was well suited for relatively long-term (about 2 months) active biomonitoring with H. aspersa snails. The snails quickly indicated the variations of MTE concentrations in their immediate environment. Therefore, the present study provides a simple but efficient field tool to evaluate MTE bioavailability and transfer.

Transfer of cadmium from plant leaves and vegetable flour to the snail Helix aspersa: bioaccumulation and effects.

Juvenile Helix aspersa snails were exposed for 4 weeks to fresh rape leaves (Brassica napus), contaminated by simulating superficial deposits of increasing concentrations of cadmium (Cd). The Cd concentration in leaves was 0.1 in control and 38.4, 93.1, and 177.2 microg x g(-1) (dry mass) in Cd-treated food. The concentration in snail tissues increased with increasing Cd concentrations in the food. The bioaccumulation factors ranged from 4.8 (control) to 2.4 (highest exposed group), indicating a biomagnification of Cd in this food chain. The growth of the snails treated with Cd was reduced by 17, 24, and 43% respectively, compared to the control group. Comparison of these results with those obtained with snails exposed to similar Cd concentrations in a vegetable flour revealed that accumulation and effects were relatively consistent, demonstrating a comparable bioavailability of Cd in the two diets. Tests using growing H. aspersa snails exposed to metals in flour or fresh leaves can be useful for risk assessment purposes.

Effects of dimethoate on snail B-esterase and growth as a function of dose, time and exposure route in a laboratory bioassay.

The aim was to study the effects of dimethoate on enzymatic targets and on the growth of Helix aspersa for different times and modes of exposure under laboratory conditions. Young snails were exposed to increasing dimethoate concentrations in the food (D.exp) or in an artificial substrate (S.exp) for 1, 2, 7 and 14 days. Both acetylcholinesterase (AChE) and carboxylesterase (CaE) activities were measured in the foot of the snails for each concentration and exposure time tested. Growth was evaluated after 7 days of exposure. AChE inhibition, dose-dependent for all lengths of exposure, was stronger in S.exp. AChE was more sensitive than CaE for both modes of exposure. IC50(-7) days was 38.3 micrograms g-1 in D.exp and 11.7 micrograms g-1 in S.exp for AChE and was higher than 150 micrograms g-1 in two exposure modes for CaE. AChE activity decreased from the first day to reach maximum inhibition after 7 days of exposure. As noted for B-esterase activities, growth inhibition was stronger in S.exp and was only significant for AChE inhibition of > 90%. The present results show that AChE activity could be used to give early warning of toxic effects of dimethoate in terrestrial gastropods.

Transfer and effects of cadmium in an experimental food chain involving the snail Helix aspersa and the predatory carabid beetle Chrysocarabus splendens.

The transfer and the toxic effects of Cd were studied in an experimental food chain involving the snail Helix aspersa as prey organism and one of its natural predators, the carabid beetle Chrysocarabus splendens. Juvenile snails were fed plant-based food enriched with 0, 10, 50 and 100 microg g(-1) of Cd, then were offered as prey to beetle larvae from egg hatching to pupation stage. Cd concentrations in snail tissues increased with increasing Cd concentration in food and with duration of exposure. Bioaccumulation factors ranged from 1.87 to 3.39, showing that H. aspersa snails, even in their early life stages, belong to macroconcentrator species for Cd. No significant reduction of snail consumption by beetles was found in exposed groups. Cd concentrations in beetle larvae remained very low (lower than 1 microg g(-1) for all groups), demonstrating a very effective regulation capacity in beetle larvae. However, Cd concentrations in highest exposed groups were higher than those found in control groups. Cd contents in adult beetles were lower than in larvae, showing a loss of Cd during metamorphosis. Despite the low Cd concentrations found in beetles, their exposure to Cd contaminated snails led to 31% of mortality, which occurred only during pupation and for the highest exposure level. No clear sublethal effects were found. These results showed that snails inhabiting heavily polluted areas may represent a risk of secondary poisoning for predatory invertebrates and provided quantitative data on the transfer of Cd between two compartments of a terrestrial food chain.

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

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.

Standardized growth toxicity testing (Cu, Zn, Pb, and pentachlorophenol) with Helix aspersa.

Juvenile Helix aspersa (1 month, 1 g) were exposed for 4 weeks to food contaminated with copper, zinc, lead, and pentachlorophenol. At concentrations observed in contaminated soils, two essential metals at low levels (Cu and Zn) had a dose-dependent sublethal action on growth. Copper inhibited growth dose-dependently between 1000 and 2000 microg small middle dotg(-1) (EC(50)=1200 microg small middle dotg(-1)), whereas zinc had a toxic effect from 4000 microg small middle dotg(-1) (EC(50)=5500 microg small middle dotg(-1)) on. Lead, a nonessential metal, had no negative effect on growth, unlike cadmium (EC(50)=140 microg small middle dotg(-1)), as reported previously. Pentachlorophenol inhibited growth at a concentration of 500 microg small middle dotg(-1) from the fourth week and 1000 microg small middle dotg(-1) from the first week on. The results obtained with these key organisms in the food chain (consumers) complement those obtained with other land invertebrates (earthworms, springtails, wood-lice, etc.). The findings of the present study and those of earlier studies indicate that juvenile snails are useful organisms for testing the sublethal toxicity of chemicals acting via the food, i.e., the main route of toxicant uptake in land animals.

Growing snails used as sentinels to evaluate terrestrial environment contamination by trace elements.

Young garden snails (Helix aspersa) reared in standard conditions (aged two months, mean weight 4.6 +/- 0.5 g) set as sentinels in cages laid on the soil for four weeks, give data for biomonitoring the environmental impact of chemicals on soil ecosystems in the field. The survival and the growth of the snails are influenced by the nature of the biotope and the level of the pollutants. Assay of cadmium, copper, lead and zinc bioaccumulated in the tissues of the sentinel snails provides information on the bioavailability of metals in the environment. The encagement model, little used for terrestrial species, can be useful in monitoring (specific and global endpoints) metal pollution of the environment in reference to the trophic level of the primary consumers. Active biomonitoring is positively compared with the passive biomonitoring.