RISK ASSESSMENT OF HEAVY METALS IN CROPS AND SOIL FROM A DUMPSITE IN RUMUOLUMENI, PORT HARCOURT

The study investigated the concentration and risk of some heavy metals lead, cobalt, cadmium, nickel, chromium, arsenic, zinc and iron in waterleaf (Talinum triangulare), fluted pumpkin (Telfairia occidentalis), cassava tuber (Manihot esculenta crantz) and soil from the dumpsite in Rumuolumeni, Port Harcourt. The result indicated that heavy metal contamination was of the order iron>zinc>chromium>nickel>lead>cobalt>cadmium>arsenic. The highest values for soil were for iron (80.00±1.070 mg/Kg) and zinc (14.91±0.197 mg/Kg), while the least was arsenic (0.014±0.050 mg/Kg). Cassava tuber had highest levels in iron (61.80±2.038 mg/Kg) and zinc (11.03±0.107 mg/kg), with the lowest levels in arsenic (0.004±0.005 mg/Kg). In fluted pumpkin, iron (43.15±0.881 mg/Kg) and zinc (8.979±0.193 mg/Kg) were highest but cobalt and cadmium were not detected. Iron (37.72±1.962 mg/Kg) and zinc (6.797±0.208 mg/Kg) had the highest concentration in waterleaf but arsenic was not detected. Zinc, chromium, and nickel were higher than the WHO permissible limit. The transfer factor from soil to plants was as high as 75-90%, especially for cassava tuber. The enrichment factor revealed that the contamination is of anthropogenic sources except for arsenic, cobalt and lead in some samples. The non-carcinogenic risk showed that the highest risk was for chromium and iron, while cobalt and lead pose risk for cassava tubers. The risks due to soil ingestion were relatively high for carcinogenic metals like lead (1.2E-4), cadmium (1.2E-4), nickel (2.6E-2) and chromium (1.2E-2). These values are higher than the benchmark of 10-4- 10-6 set for management decisions by USEPA for carcinogenic substances in the environment. The other heavy metals with high carcinogenic risk are nickel and chromium in waterleaf, fluted pumpkin, and cassava with estimated values ranging from 3.7E-3 to 2.3E-2. From the findings, the risks associated with consuming food planted within the dumpsite environment are high and should be stopped.