Risk assessment of glyphosate and malathion pollution and their potential impact on Oreochromis niloticus: role of organic selenium supplementation

Abstract

A field survey was conducted on five fish farms to trace glyphosate and malathion pollution with some physicochemical parameters. A precise half-life time, LC₅₀-96h, of these agrochemicals on Oreochromis niloticus, as well as chronic exposure with organic selenium (OS) supplementation, were experimentally investigated. Oreochromis niloticus was subjected to the following: (negative control); (2 mg L^-1 glyphosate); (0.5 mg L^-1 malathion); (glyphosate 1.6 mg L^-1 and 0.3 mg L^-1 malathion); (glyphosate 2 mg L^-1 and OS 0.8 g kg^-1 diet); (malathion 0.5 mg L^-1 and OS 0.8 g kg^-1 diet) and (glyphosate 1.6 mg L^-1; malathion 0.3 mg L^-1 and OS 0.8 g kg^-1 diet). Furthermore, data from the analyzed pond revealed a medium risk quotient (RQ) for both agrochemicals. The detected agrochemicals were related to their application, and vegetation type surrounding the farms, also their biodegradation was correlated to water pH, temperature, and salinity. Glyphosate and malathion had half-lives of 2.8 and 2.3 days and LC₅₀-96h of 2.331 and 0.738 mg L^-1, respectively. The severest nervous symptoms; increased oxidative stress markers, as well as high bacterial count in the livers and kidneys of fish challenged with Aeromonas hydrophila, were observed in the combined exposure, followed by a single exposure to malathion and then glyphosate. Organic selenium mitigated these impacts.

Figure 1

Experimental groups design illustration.

Figure 2

Probability for half-life of Glyphosate and Malathion mg L⁻¹ in natural log days using Probit analysis.

Figure 3

Vitality and behavioral changes scoring of Oreochromis niloticus exposed to glyphosate and/ or malathion with role of organic selenium. Friedman Test showed a statistically significant difference in the detected symptoms between the different treatments, χ²(2) = 22.75, P < 0.001, with a mean rank of 4.21, 3.79, 3.57,3.50, 3.29 and 2.64 for jerky movement, gasping, off food, loss of equilibrium, erected fin and body pigmentation. A Kruskal–Wallis H test showed that there was a statistically significant difference in the detected symptoms between the different treatments, χ²(2) = 20, P < 0.02, with the same mean rank score of negative control and OS treated groups in all detected signs. (A) Vitality and behavioral changes. (B) fish suffered from body pigmentation.

Figure 4

Cumulative survival rate for fish in all experimental groups exposed to glyphosate and or malathion intoxication in absent and presence of organic selenium.

Figure 5

Glyphosate and /or malathion intoxication on oxidative stress biomarkers in Oreochromis niloticus with organic selenium supplementation. Means with different superscripts are statistically different (P < 0.05). (A) Malondialdehyde (MDA) in liver and kidney tissues. (B) Superoxide dismutase (SOD) in liver and kidney tissues. (C) Glutathione peroxidase (GPX) in liver and kidney tissues.

Figure 6

Symptoms in challenged Oreochromis niloticus with Aeromonas hydrophila. (A) petechial hemorrhage at pectoral fin and operculum in malathion in fish exposed to combined chemicals. (B) erythema and Redding of mouth in glyphosate exposed fish. (C,D) enlarged liver with congestion in gills in malathion and glyphosate exposed fish, respectively.