Giant Land Snails Reveal Hidden Limits of Soil Metal Contamination in Abidjan

In the sprawling peri-urban districts of Abidjan, where industry, agriculture and informal waste disposal press against remnant green spaces, the soils carry a chemical signature of rapid urbanization. A new study published in the Archives of Environmental Contamination and Toxicology has now traced what happens when that signature meets one of West Africa’s most familiar and most consumed animals: the giant land snails Achatina achatina and Archachatina ventricosa. The research, led by Gisette Affoué Kouadio of the University of Nangui Abrogoua together with colleagues in Côte d’Ivoire and France, examined thirteen contrasting soils across the Abidjan district and measured how iron, copper and zinc moved from those soils into two snail tissues, the hepatopancreas and the edible flesh. The findings challenge a deceptively simple assumption that has underpinned much contamination monitoring: that dirtier soil automatically means a dirtier animal.

The team’s starting point was a practical gap. Ecotoxicological risk assessment tools have been built and validated largely in temperate Europe, where the garden snail Cantareus aspersum serves as a standardized test organism enshrined in ISO guidelines. Tropical West Africa, with its distinct soils, climates and faunas, has had no equivalent sentinel. Yet the giant Achatininae snails are ideal candidates. They are large, abundant, sedentary, easy to sample, and they occupy a central place in local food culture, where they are traditionally eaten whole. Any metal that accumulates in their tissues therefore travels directly into the human food chain, making these animals simultaneously an ecological indicator and a public health concern.

To quantify the pressure that contamination exerts on each site, the researchers applied a Toxic Pressure Index, or TPI, an integrative metric previously developed for managing polluted sites, which aggregates the concentrations of multiple metals relative to reference values. Crucially, they computed the TPI twice: once for the soil at each site and once for the snail tissues collected there. If external contamination drove internal burden in a straightforward way, the two indices should rise and fall together. They did not. Across every tissue-species combination, the study found no significant relationship between soil TPI and tissue TPI, a systematic decoupling between what is in the ground and what ends up inside the animal.

The scale of soil contamination itself was striking. Zinc dominated the toxic pressure at every one of the thirteen sites, and pseudo-total zinc concentrations reached as high as 37,656 milligrams per kilogram of soil, a figure far exceeding typical background levels. Such values reflect the diffuse loading that peri-urban tropical soils receive from industrial emissions, vehicle traffic, waste burning and agricultural inputs. But pseudo-total concentrations measure everything that strong acid digestion can extract from the soil, not the fraction that an animal’s gut can actually dissolve and absorb. The study’s central result is precisely that this distinction matters enormously, and that it matters in a patterned, quantifiable way.

That pattern emerged from the bioconcentration factors, or BCFs, calculated for every combination of metal, tissue and species. The BCF expresses the ratio of a metal’s concentration in snail tissue to its concentration in the soil, and values above one indicate bioconcentration, while values below one indicate biodilution. For iron and zinc, the verdict was unambiguous: biodilution occurred universally, in every tissue and in both species. Even more telling, log-log regression slopes for zinc in the flesh of both species approached minus one, a mathematical signature of strict homeostatic regulation. In practical terms, as soil zinc concentration increased, the snails’ internal zinc concentration barely moved, as though a physiological ceiling capped how much of the metal their bodies would tolerate regardless of external loading.

Copper told a different story. It was the only element consistently bioconcentrated above unity, and only in the hepatopancreas, the snail’s equivalent of a liver and digestive gland combined. This occurred at eight of the thirteen sites for Achatina achatina and eleven of thirteen for Archachatina ventricosa. The explanation is physiological rather than toxicological: copper is an essential trace element, required for respiratory pigments and enzymatic functions, and the hepatopancreas actively accumulates and stores it. The finding echoes decades of work on temperate helicid snails, in which metallothionein proteins and organ-specific storage have long been shown to separate essential metals, which are regulated and sequestered, from non-essential ones, which are more passively handled. The Abidjan study extends that framework to a tropical lineage for the first time with field data.

Tissue identity proved to be the strongest single determinant of accumulation. For all three metals and both species, BCF values were significantly higher in the hepatopancreas than in the flesh, with Wilcoxon tests returning p-values below 0.01 throughout. Hepatopancreas-to-flesh ratios ranged from threefold to twenty-twofold, meaning that the organ responsible for detoxification can carry an internal burden an order of magnitude greater than the muscle tissue that people typically eat. Yet the two compartments are not independent. The study detected a significant positive correlation between hepatopancreatic and flesh BCFs for copper in both species, which matters directly for consumer exposure: because these snails are traditionally consumed whole, including the hepatopancreas, the organ that concentrates metals the most is also on the plate.

Perhaps the most sobering result is what the researchers could not find. Using multivariate regression modelling, they attempted to build ecologically coherent models that combined soil metal concentrations with soil physicochemical properties, such as pH, texture and organic matter, as joint predictors of bioconcentration. The models failed. No combination of measured soil characteristics reliably predicted how much metal ended up in the snails. This null result carries a pointed message for risk assessment practice: knowing a soil’s total metal content, and even its chemistry, is not sufficient to forecast biological uptake. Bioavailability, governed by processes that pseudo-total digestion cannot capture, remains the critical and stubbornly site-specific variable. It also suggests that temperate-derived predictive models cannot simply be transplanted into tropical contexts without recalibration.

Encouragingly for the use of these snails as sentinels, the two species behaved remarkably similarly. No significant interspecific differences in BCF were detected, suggesting that Achatina achatina and Archachatina ventricosa employ broadly comparable metal regulation strategies. For monitoring programs in West Africa, this means either species could serve as a bioindicator, and results from one may be cautiously generalized to the other. Given that both are harvested from the wild and sold in local markets, the convergence also simplifies the task of translating ecological measurements into dietary exposure estimates for communities living along contamination gradients.

The broader implications reach well beyond Abidjan. Peri-urban soils across rapidly expanding West African cities face mounting metal inputs from the same mix of industrial, urban and agricultural sources, while formal ecotoxicological infrastructure remains scarce. This study supplies both a warning and a method. The warning is that soil contamination maps alone cannot identify which animals, and therefore which meals, carry the greatest internal burdens, and that homeostatic regulation can mask exposure in ways that total soil chemistry never reveals. The method is a paired index approach, comparing external toxic pressure with internal tissue burden, that can be replicated wherever large, edible, sedentary gastropods occur. As cities like Abidjan continue to grow into their surrounding landscapes, the humble giant snail may prove to be one of the most informative, and most consequential, sentinels of environmental health in the tropics.

Subject of Research: Bioaccumulation of iron, copper and zinc in tropical land snails across a peri-urban contamination gradient in Abidjan, Côte d'Ivoire

Article Title: From Soil Contamination to Internal Metal Burden: Drivers of Fe, Cu and Zn Bioaccumulation in Tropical Achatininae Across a Peri-Urban Contamination Gradient (Abidjan, Côte d’Ivoire)

Article References: Kouadio, G. A., Louzon, M., Memel, J.-D., & Katta, E. L. (2026). From Soil Contamination to Internal Metal Burden: Drivers of Fe, Cu and Zn Bioaccumulation in Tropical Achatininae Across a Peri-Urban Contamination Gradient (Abidjan, Côte d’Ivoire). Archives of Environmental Contamination and Toxicology, 91(3), Article 21. https://doi.org/10.1007/s00244-026-01222-4

Image Credits: AI Generated

DOI: 10.1007/s00244-026-01222-4

Keywords: land snails, bioaccumulation, heavy metals, soil contamination, Abidjan, Côte d'Ivoire, ecotoxicology, copper, zinc, iron, peri-urban, food safety