Dose-dependent effects of lead and cadmium and the influence of soil properties on their uptake by Helix aspersa: an ecotoxicity test approach

Cadmium toxicity to and accumulation in a soil collembolan (Folsomia candida): major factors and prediction using a back-propagation neural network model

Accurate prediction of cadmium (Cd) ecotoxicity to and accumulation in soil biota is important in soil health. However, very limited information on Cd ecotoxicity on naturally contaminated soils. Herein, we investigated soil Cd ecotoxicity using Folsomia candida, a standard single-species test animal, in 28 naturally Cd-contaminated soils, and the back-propagation neural network (BPNN) model was used to predict Cd ecotoxicity to and accumulation in F. candida. Soil total Cd and pH were the primary soil properties affecting Cd toxicity. However, soil pH was the main factor when the total Cd concentration was < 3 mg kg-1. Interestingly, correlation analysis and the K-spiked test confirmed nutrient potassium (K) was essential for Cd accumulation, highlighting the significance of studying K in Cd accumulation. The BPNN model showed greater prediction accuracy of collembolan survival rate (R2 = 0.797), reproduction inhibitory rate (R2 = 0.827), body Cd concentration (R2 = 0.961), and Cd bioaccumulation factor (R2 = 0.964) than multiple linear regression models. Then the developed BPNN model was used to predict Cd ecological risks in 57 soils in southern China. Compared to multiple linear regression models, the BPNN models can better identify high-risk regions. This study highlights the potential of BPNN as a novel and rapid tool for the evaluation and monitoring of Cd ecotoxicity in naturally contaminated soils.

Can mollusks or insects serve as bioindicators of the risk element polluted area? Gastropods (Gastropoda) versus leaf beetles (Coleoptera: Chrysomelidae)

Two groups of invertebrates, terrestrial mollusks (Gastropoda) and Chrysomela populi leaf beetles (Coleoptera: Chrysomelidae), were sampled to estimate the suitability of these organisms as bioindicators of risk element pollution (predominantly Cd, Pb, and Zn) alongside the risk element concentration gradient in the contaminated area (former mining/smelting areas in the vicinity of Příbram city, Central Bohemia, Czech Republic). The individuals representing ten species of terrestrial snails and imagoes of C. populi were collected manually at five sampling sites, differing in the level of soil contamination with risk elements. The findings showed high variability of the results regardless of the element determined, animal species, and sampling location. Among the elements, higher accumulation ability was observed for Cd and Zn, given the higher bioaccessibility of these elements in soils compared to Pb, Cr, and Cu. Higher Cd and Zn accumulation in the soft tissues of gastropods (without any statistically significant differences among the species) compared to C. populi was also recorded. Medians of the bioaccumulation factors (BAFs) reached up to 33.2 for Cd and 5.8 for Zn, in gastropods while reaching up to 3.4 for Cd, and 2.3 for Zn, for C. populi. For both groups of organisms, paradoxically, a higher rate of accumulation of risk elements was observed in all analyzed organisms in sites with lower soil contamination compared to heavily contaminated sites. This indicated the ability of the organisms living in extreme conditions to avoid the uptake of these elements or to move among areas of different contamination levels. Thus, terrestrial gastropods and C. populi proved to be unsuitable bioindicators for assessing soil pollution.

Toxicity and accumulation of lead and cadmium in the land snail, Archachatina papyracea, in a tropical Alfisol from Southwestern Nigeria

Snails are an important link in the transfer of contaminants, especially metals in the food chain. Yet, few studies have examined the toxicity and accumulation of metals in snails in the tropics. This study assessed the toxicity and accumulation of two non-essential metals (cadmium and lead) to the tropical snail Archachatina papyracea. Specimens of the snail A. papyracea were exposed in a loamy soil collected from Ile-Ife, Nigeria and spiked with varying concentrations of Cd and Pb over 28 days. Survival and weight change of snails were monitored weekly, while tissue accumulation was assessed at the end of the 28-day period. Survival was a more sensitive endpoint than the weight change of snails. The Cd median lethal concentration (LC50) value was 93 ± 4.4 mg/kg, while the median effect concentration (EC50) for snail weight change was 131 ± 41 mg/kg. For Pb, LC50 value was 1121 ± 457 mg/kg, while the EC50 value for weight change was higher at 4541 ± 1180 mg/kg. Therefore, Cd was a factor of about 10 to 30 × more toxic than Pb, consistent with findings on the relative toxicity of Cd and Pb to other soil organisms, including earthworms, springtails, and mites. Although not included initially as an endpoint, egg production in the snails decreased with increasing Cd and Pb concentrations in the substrate. Metal analysis of the foot and visceral mass of surviving snails showed progressive accumulation of Cd and Pb as concentration increased, showing the tendency to use body residue of A. papyracea as an indicator of metal pollution. It further suggests the role of this snail species in above-ground metal transfer in the food chain and highlights the potential danger for human consumption.