Determination of Selected Heavy Metals in Sugarcane (Saccharum Sp) Grown along Ngong Tributary of Nairobi River

Abstract

The transfer of heavy metals from soil or water to plants can pose a health hazard to humans if such plants and their products are consumed. Heavy metals from industrial waste are often deposited in land and water bodies neighbouring the urban and industrial areas. Nairobi river is one such area. The study aimed at establishing heavy metal contamination and safety of consumption of sugarcanes grown along Ngong tributary of Nairobi river. Sugarcane, soil, and water were randomly sampled from the upstream, middle stream, downstream and control points during the wet months of October and November 2016 and dry month of January 2017. Kisii region was the control point. Levels of copper, lead, cadmium, chromium, iron, manganese and zinc in juice soil and water were determined by Atomic absorption spectrophotometer. Transfer factor was determined by comparing levels in juice and soil. Heavy metals analysis, sensory evaluation and health risk assessment of sugarcane juice vendored from various selling joints of fresh sugarcane juice within Kibera, Kayole, Njiru, Kariobangi, and Mukuru areas located along this tributary as well as Kisii region were determined. Sensory evaluation was done through just about scale and preference test while heavy metal concentration of vendored juice was done by atomic absorption spectrophotometer. The results showed that levels of iron, chromium, and lead for sugarcane juice collected along Ngong tributary were higher than safe limits recommended by WHO. In vendored juice chromium, lead, iron, and manganese levels werehigher than WHO recommended limits. In water samples, levels of chromium, iron, lead and manganese were more elevated than WHO recommended levels. The concentration of copper, chromium, iron, manganese, lead, zinc, and cadmium for juice samples ranged from undetected levels to 3.61mg/l. Water samples' heavy metal concentration ranged from undetectable levels to 3.5mg/l while soil samples ranged from undetected levels to 295.2mg/kg. Vendored juice heavy metal levels ranged from undetected levels to 4.74mg/l. There were significant differences (p<0.05) of the levels of the heavy metals in upstream, middle stream, downstream as well as control region for sugarcane juice, soil and water. There were also significant differences in heavy metal levels in slums along Ngong tributary and control region for vendored sugarcane juices P<0.05. The most preferred vendored juice had significantly lower concentrations of all heavy metals (P<0.05) apart from zinc. The least preferred juice had significantly higher levels of manganese, iron, chromium and copper. Most preferred sugarcane juice in sensory evaluation scored highly in aroma and level of sweetness compared to the least preferred, which was most salty. This result indicated that higher levels of heavy metals in juice affected their preference. The transfer factor ranged from 0 to 0.106 while the total estimated daily intakes (EDI) of juice for adults ranged between 0.01mg/kg/d and 0.03mg/kg/d while for children were 0.02mg/kg/d and 0.07mg/kg/d. Total hazard quotients (TTHQ) for adults were 0.14 and 0.3 while those of children ranged between 0.34 and 0.7. In general, most heavy metals concentration were higher than WHO recommended limits in river water, soil and sugarcane juice. However, the risk of consumption of heavy metals from vendored juices in the sampled regions was low compared to TTHQ level of 1 that is considered a high risk.