Changes in concentration of DTPA-extractable forms of metals in response to soil treatment with variable seashell doses

Seashells piled in coastal areas worldwide, particularly near commercial mollusk farms, may pose a substantial environmental and health risk. Utilizing seashell waste (SW) as a natural liming material represents a meaningful contribution to the sustainable development of the aquaculture industry through resource recovery. This study assessed the effects of adding various doses of finely ground SW to acidic agricultural soil with elevated total concentration of Cu (219.2 mg/kg) on the bioavailability of selected metals (Cu, Zn, Fe, Mn, Co, Pb, Ni, and Cd). The concentration of DTPA-extracted forms of Cu and other elements decreased significantly with the increase in SW dose from 0.15% to 2%, whereas differences between 2% and 5% treatments were not significant. The association of metals' bioavailability with the agrochemical properties of control and treated soil samples revealed the leading influence of soil pH. Furthermore, the DTPA-extracted amounts of Cu and Zn were negatively correlated with carbonate and organic carbon content, and bioavailable Zn forms were negatively correlated with the content of accessible phosphorus. As a cost-effective, sustainable, and renewable source of calcium carbonate, organic carbon, and available phosphorus, SW is a candidate material for acidic soil amelioration, including the immobilization of a range of toxic and potentially toxic metals. However, the study's results underline that SW dose optimization through preliminary tests is a necessary research component that requires observing soil fertility parameters, particularly the status of essential metals.