Tracing heavy metals in tomato plants watered with synthetic wastewater treated with a bacterial coated calcium alginate nanobiosorbent

Rama, Haripriya
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Heavy metals accumulate in soils and crops irrigated with acid mine decant (AMD) polluted water, posing environmental health risks. The dead bacterial biomass of Micrococcus luteus and Enterobacter xiangfangensis Pb204 were previously identified as effective biosorbents for the treatment of multi-metal systems under neutral conditions. The study aimed to treat AMD waters with free and immobilized bacterial biosorbent and determine the suitability of the treated water for agricultural purposes. Acid mine decants representative of the Central and Witwatersrand basin, Gauteng, South Africa were neutralized with limestone or sodium hydroxide. Limestone neutralized AMD samples were treated with M. luteus and E. xiangfangensis Pb204 individually or in combination to determine the most effective biosorbent. Subsequently, M. luteus was immobilized onto calcium alginate nanoparticles (CANPs) forming a nanobiosorbent for treatment of limestone neutralized AMD samples. The biosorption profile of the nanobiosorbent was compared to free CANPs, M. luteus and a mixture of M. luteus biosorbent with free CANPs, by quantifying metal concentrations using inductively coupled plasma optical-emission spectrometry (ICPOES) and inductively coupled plasma-mass spectrometry (ICP-MS). Four groups of tomato plants (Rodade variety) were grown under controlled conditions and irrigated with tap water, untreated AMD water or AMD water treated with free biosorbent or nanobiosorbent, respectively. Plants from all groups that developed fruit (except for those irrigated with nanobiosorbent treated water) displayed stunted growth during the fruiting stage. Metal accumulation in the plant structures occurred in the order flowers>roots>stems>leaves=fruit. Most metals in the fruits exceeded the recommended maximum daily adult intake or the acceptable limits for human consumption even in the group irrigated with tap water. The commercial potting soil used to grow the plants contained elevated levels of Mn (1327.92 mg/kg) and Cu (17.11 mg/kg) which remained high in the soil from all treatment groups. These findings show that although treatment with M. luteus biosorbent or nanobiosorbent lowered metal concentrations in AMD, irrigating plants with the treated water resulted in the stunted development of fruit which was unfit for human consumption.
A dissertation submitted in fulfilment of the requirements for the degree Master of Science in Molecular and Cell Biology in the Faculty of Science, University of the Witwatersrand, Johannesburg, 2019
Rama, Haripriya (2019) Tracing heavy metals in tomato plants watered with synthetic wastewater treated with a bacterial coated calcium alginate nanobiosorbent, University of the Witwatersrand, Johannesburg,