Phytotoxic Effects Of Heavy Metals-Enriched Water Irrigation On Food Crops Using A Closed Hydroponic System

• Main Author: Chow, Yuh Nien
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: T Technology; TA1-2040 Engineering (General). Civil engineering (General)
• Online Access: http://eprints.usm.my/47855/1/Phytotoxic%20Effects%20Of%20Heavy%20Metals-Enriched%20Water%20Irrigation%20On%20Food%20Crops%20Using%20A%20Closed%20Hydroponic%20System.pdf; http://eprints.usm.my/47855/
• Institution: Universiti Sains Malaysia

The issues of food and water security have conventionally been addressed independently, and to date, their nexus has emerged to be the most intricate global agenda. Today, wastewater irrigation has emerged to be a widespread strategy to fulfil the pressing need of non-conventional water resources. These discharges carry toxic elements, exceeding the maximum allowable limits, suggesting the possible risks to food crops and food chain. Heavy metals are the most carcinogenic, teratogenic and mutagenic constituents, accumulating in the irrigation water. Trivalent chromium [Cr (III)], lead [Pb (II)] and nickel [Ni (II)] are the most insidious pollutants, ascribed to their complex electronic chemistry, non-biodegradability, solubility and mobility. This study aimed to investigate the complex interconnection of metals-enriched water irrigation on Vigna radiata, Ipomoea aquatica and Brassica chinensis in relation to the physical growth; physiological characteristics: photosynthetic pigments, proline, antioxidative response [guaiacol peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX)], antioxidant capacities and morphological characteristics. The toxicity implications were evaluated using in vitro bioassays. Metals-enriched water irrigation adversely induced significant concentration- and duration-dependent reductions in the elongation of roots and shoots; with Cr (III) exerted the highest inhibition in Vigna radiata and Brassica chinensis, denoted the reduction of 68.04% and 75.69% for root and shoot. Ipomoea aquatica was specifically sensitive to Ni (II), with the highest root and shoot inhibition of 83.78% and 87.33%. Chlorophyll-a, chlorophyll-b, and carotenoid contents were significantly reduced, up to 83.92%, 75.86%, and 63%. Profound lipid peroxidation (170.30%) and rising proline content (201.08%) were complementary with the pronounced alterations for POD, APX and CAT activities. The marked suppressions of antioxidant activities above the threshold levels of 0.50 mM Pb (II), 0.20 mM Cr (III) and 0.05 mM Ni (II) in the plant models indicated that the antioxidant defense machinery could no longer protect the plant systems against the oxidative damages. These disturbances corroborated with the xylem and phloem distortion, and stomata disruption. Significant cytotoxic effect with 50% reduction in HepG2 cell viability was noted at 0.20 mM Pb (II), 0.40 mM Ni (II) and 1.20 mM Cr (III). Genotoxic effects on DNA tail moment and tail damage were observed at the lowest concentration of 0.04 μg/mL. Conclusively, the oxidative stress-related health threats associated with the deteriorating effects on the food crops could be exacerbated by a wide scale unregulated metals-polluted wastewater irrigation practice, and place alarming threats to the sustainability of water-food nexus.