Abstract
Intake of vegetables grown in heavy metals contaminated soils is one of the most common food chain routes for exposure of human. For this purpose, this research aimed at evaluating the concentration of heavy metals (cadmium-Cd, lead-Pb and zinc-Zn) in vegetables such as spinach (S), lettuce (L), and onion (O), irrigated with two different wastewater sources in Kano State Nigeria. Atomic Absorption Spectrophotometric analysis (AAS) was used in this research to determine the metal levels. Zn (0.17-0.12 mg/l) was detected in the wastewater, as well as in the irrigated soil (8.36-33.64 mg/kg), while Cd and Pb were not detected in both the wastewater and irrigated soils. Furthermore, between (1.50-27.05 mg/kg) of Zn was detected in the assayed vegetables (S, L and O). However, there was no significant difference (p<0.05) between the Zn content of the two wastewater sites. Lactuca sativa was observed to have the highest Zn concentration (27.5 mg/kg) in site A, while Spinacia oleracea had the lowest Zn concentration (1.5 mg/kg). Zn levels in all the samples analysed in this study were below the permissible limit of 100 mg/kg in vegetables, 50 mg/kg in soil and 5mg/l in wastewater set by FAO/WHO. However, Pb and Cd were not detected in all the samples. Bioaccumulation factor was found ranging from 0.32-41.17 mg/kg and the pollution index ranged from (0.46-1.80 µg g-1). This indicated potential health risk from Zn in people who are consuming these vegetables for long period of time due to biomagnification. This research suggested that frequent test should be carried out to monitor the accumulation and, farmers should be sensitized on the importance of treating irrigation water before agricultural usage.
Highlights
Shortage of irrigation water, especially in the tropical savannah regions of Nigeria have affected crop production
Since heavy metals contents of wastewaters depend on production company and type of its by-products, the presence of Zn in the wastewater indicated that the company might have likely make use of Zn oxides in their production
The presence of high concentration of heavy metals (Zn, Cd and Pb) irrigation water may lead to contamination of growing soil and can be uptake and accumulated by growing vegetables in their various body sections
Summary
Especially in the tropical savannah regions of Nigeria have affected crop production. This problem became serious because of the increasing urbanization and industrialization in this region. In order to improve crop productivity through improved irrigation, local farmers resulted to utilizing immense amount of wastewaters released from industries for watering vegetables, most especially in industrial regions, due to water scarcity issues (Mashiatullah et al, 2005; Hamid et al, 2016). Wastewater have been documented to contain heavy metals such as zinc (Zn), iron (Fe), lead (Pb), copper (Cu), cadmium (Cd) and Received: 26 Jan 2021. Received in revised form: 08 Feb 2021. From Volume 13, Issue 1, 2021, Notulae Scientia Biologicae journal will use article numbers in place of the traditional method of continuous pagination through the volume
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