Tissue-Level Biomarkers in Sentinel Slugs as Cost-Effective Tools to Assess Metal Pollution in Soils

Abstract

In previous laboratory experiments, slugs were shown to be sensitive to metal pollution. Therefore, they might be invaluable instruments for biological assessment of soil pollution. The present investigation was carried out to validate previous laboratory results in a field study. Slugs were collected from an abandoned copper mine (Parys mountain top, PMT), from a site 7 km away from the mine (Parys mountain bottom, PMB), and from a clean site (Snowdonia Cwm Idwal, SCI) in Wales in early July 1994. Whole soft body and digestive gland Cd, Cu, and Zn concentrations were measured by means of atomic absorption spectrophotometry (AAS). The digestive gland was the main tissue for metal accumulation, with significant differences in tissue metal levels between samples from different sites. PMB presented the highest Cd and Zn levels and the highest Cu levels were found at PMT. In addition, metals were demonstrated in situ by autometallography as black silver deposits (BSD) on histological sections of digestive gland tissue. The extent of BSD within lysosomes of digestive cells was closely related to metal levels determined by AAS. Histochemistry revealed that Ca metabolism and structural and reserve connective tissues might be altered in slugs living in metal-polluted soils. Finally, tissue-level biomarkers of biological effect [mean epithelial thickness (MET), mean diverticular radius (MDR), mean luminal radius (MLR), MET/MDR and MLR/MET] were quantified by image analysis of digestive gland histological sections stained with hematoxylin-eosin. MET and MDR values of slugs collected from SCI were high, while slugs from PMB presented low MLR/MET associated with environmental stress induced by metal exposure. We conclude that exposure and effect biomarkers recorded in sentinel slugs could be sensitive, quick, and cheap indices of metal pollution in soils. A Slug Watch monitoring program could be developed similar to the Mussel Watch program, which is currently applied to assess environmental quality in coastal and estuarine areas.

Metal accumulation and apoptosis in the alimentary canal of Lumbricus terrestris as a metal biomarker

“…Analogous adaptations in the digestive epithelium thickness of mollusks have been previously reported as an effect of changes in environmental quality as increased bioavailability of pollutants (Lowe et al 1981;Vega et al 1989;Marigo´mez et al 1990Marigo´mez et al , 1991Marigo´mez et al , 1992Cajaraville et al 1992). Marigo´mez et al (1996Marigo´mez et al ( , 1997 also found a clear evidence of severe adaptative changes in the digestive gland of mollusks following long-term/ chronic exposure to pollutants. According to Morgan et al (2002), the earthworm chloragocyte suffers morphological alterations to cope with larger quantities of metals.…”

Morphometry of the epidermis of an invasive megascoelecid earthworm (Amynthas gracilis, Kinberg 1867) inhabiting actively volcanic soils in the Azores archipelago

“…Such structural changes can be assessed morphometrically, a technique that is sufficiently sensitive to detect epithelial thinning due to environmental stress in the digestive epithelia and reproductive tissues of several invertebrates (Vega et al, 1989;Marigomez et al, 1998;Siekierska and Urbanska-Jasik, 2002). Morphological alterations are not uncommon among organisms exposed to extreme environments.…”

Bioaccumulation and histopathological changes of the digestive gland of the land snailEobania vermiculata(Mollusca: Gastropoda), as biomarkers of terrestrial heavy metal pollution in Taif city

“…Land snails such as Helix aspersa and Arianta arbustorum have previously been used for the estimation of urban (Regoli et al 2006;Itziou & Dimitrids 2009) or industrial (Marigomez et al 1998) pollution, due to their ability to accumulate trace metals in their tissues (Beeby & Richmond 2002;Viard et al 2004). …”