Evaluation of Heavy Metals from Cocoa Growing Soils of Trinidad & Tobago.

While it has been well established that excess cadmium exposure produces adverse health effects on human beings, researchers are still pursuing efforts to answer questions relating to exposure levels and also entry pathways into food chain. As a heavy metal found in soil, cadmium gets entry into a variety of food plants including cocoa. Cadmium levels in cocoa have raised the concern of the researchers, and regulatory agencies are seeking to regulate the amount of the cadmium in various foodstuffs by imposing maximum allowable levels. An initial step in our quest to reach these goals is to study the extractability of cadmium and other heavy metals on selected Cocoa-growing soils representing 12 major soil classes of Trinidad and Tobago. For this study, a total of 30 soil samples were collected from island-wide representative cocoa growers’ farms and another 15 representative soil samples from a 6.21 ha farm of “Home for World Gene Bank for Cocoa” of University of West Indies [UWI]. These samples were used to study the extractability of Cd, Cr, Ni and Pb using 7 common chemical extractants described in literature. Results of this study revealed that Mehlich III and DTPA extracted more heavy metals compared to other extractants. Water extracted generally less heavy metals compared to all other extractants. Extractable Ni and Pb contents are comparatively higher than that of extractable Cd & Cr contents. Results also indicated that some of the soils had very high level of water-extractable heavy metal contents which can act as potential sources contributing to harmful levels in groundwater. Further studies are planned to identify chemical associations of these heavy metals in soils through ‘sequential extraction’ processes to understand the dynamics of these heavy metals and their impact on soil and water environment that could affect plant uptake.