Concentration of Trace Metals (Lead, Iron, Copper and Zinc) In Crops Harvested in Some Oil Prospecting Locations in River State, Nigeria

Concentrations of the trace metals lead, iron, copper and zinc were estimated in crops harvested in some oil prospecting locations in Rivers State, Nigeria. The locations were; Agbada-Aluu (AA), Ebocha (EB), Idu Ekpeye (IE), Obagi (OB) and Trans Amadi Layout (TA), with the Teaching and Research Farm of Rivers State University of Science and Technology, Port Harcourt as control. Crops investigated were cassava (Manihot esculenta), cocoyam (Colocasia esculenta), okra (Hibiscus esculentus), pumpkin leaves (Telfairia occidentalis) and waterleaf (Talinum traingulare). Results of the mean lead concentrations were from 1.1µg/g in cocoyam to 9.1 µg/g in okro, showing higher trends in the industrialized areas. While cocoyam had the lowest lead concentration, the concentration rest of the crops did not differ significantly from one another. Crops from locations TA, OB, IE and EB had significantly higher concentrations of lead, although IE, AA and TF were not significantly different from one another. Mean concentrations of iron were between 40 µg/g in cassava from TF, and 651 µg/g in pumpkin leaves from TA - the industrial base of Rivers State - reflecting a high level of pollution from the various industries in that location. Differences in concentration of iron in crops showed pumpkin leaves to have the highest level of iron, followed by the other green vegetables – waterleaf and okra - although no significant differences occurred between okra, cocoyam and cassava. Copper concentrations were between 4.4 µg/g in cocoyam from locations TF and 23 µg/g in pumpkin leaves from TA. Pumpkin leaves had the highest concentrations of copper, followed by okra, then waterleaf, with cocoyam and cassava having the least significant levels. Zinc concentrations in crops were between 29 µg/g in cocoyam from TF to 240 µg/g in pumpkin leaves from EB. Pumpkin leaves and okra contained the highest levels of the metal, followed by waterleaf, then cassava and finally cocoyam. In terms of location, TA, OB and EB had the highest concentrations in crops, the least occurring in TF and AA. These results reflect higher concentrations of metals in crops from the industrialized locations, with the green vegetables, particularly pumpkin leaves, having the highest uptake, while cocoyam invariably had the least. These findings give cause for concern, particularly as heavy metals are bio-accumulative in the system and portend a serious health risk to man and animals.