Soil contamination and transfer dynamics of trace metals to plants and snails in a large urban dumpsite in Northwest Morocco

Soil contamination by trace metals (TMs) has long been a major environmental issue, posing serious threats to ecosystems and human beings. This study aims to evaluate the contamination levels of soils, plants (Malva sylvestris and Nicotiana glauca), and snails (Otala spp. and Theba pisana) by Cd, Cr, Co, Cu, and Zn at a large urban dumpsite in Northwest Morocco, as well as to explore the transfer dynamics of these TMs through these dumpsite components. The results revealed high average contents of the TMs in the dumpsite soil, reaching 7.76, 38.91, 29.76, 136.77, and 477.78 mg/kg for Cd, Cr, Co, Cu, and Zn, respectively, thus exceeding the corresponding FAO and WHO limits. Plants, particularly Malva sylvestris, showed high average Zn and Cu contents of 398.43 and 64.22 mg/kg (d.w.), respectively. Although Malva sylvestris and Nicotiana glauca are not TMs accumulator species, they translocated these TMs from the soils to their aerial parts, demonstrating their adaptability to polluted environments. Meanwhile, snail species inhabiting the dumpsite accumulated high TM levels, reaching up to 18.32 and 23.02 mg/kg (d.w.) for Cd and Cr, respectively in Otala spp. Although the snail species were TMs macroconcentrators, they maintained normal functions, further demonstrating their resilience in heavily TMs-contaminated environments. According to multiple linear regression (MLR) results, TM contents in the snail soft tissues were explained mainly by the TM contents in the Malva sylvestris leaves rather than those in the soils. These findings highlight the complex dynamics of TMs transfer within dumpsite systems and raise the urgent need for effective waste management strategies to mitigate the environmental and health risks associated with TM pollution.