Cytogenotoxicity screening of source water, wastewater and treated water of drinking water treatment plants using two in vivo test systems: Allium cepa root based and Nile tilapia erythrocyte based tests.

Biological effect directed in vivo tests with model organisms are useful in assessing potential health risks associated with chemical contaminations in surface waters. This study examined the applicability of two in vivo test systems viz. plant, Allium cepa root based tests and fish, Oreochromis niloticus erythrocyte based tests for screening cytogenotoxic potential of raw source water, water treatment waste (effluents) and treated water of drinking water treatment plants (DWTPs) using two DWTPs associated with a major river in Sri Lanka. Measured physico-chemical parameters of the raw water, effluents and treated water samples complied with the respective Sri Lankan standards. In the in vivo tests, raw water induced statistically significant root growth retardation, mitodepression and chromosomal abnormalities in the root meristem of the plant and micronuclei/nuclear buds evolution and genetic damage (as reflected by comet scores) in the erythrocytes of the fish compared to the aged tap water controls signifying greater genotoxicity of the source water especially in the dry period. The effluents provoked relatively high cytogenotoxic effects on both test systems but the toxicity in most cases was considerably reduced to the raw water level with the effluent dilution (1:8). In vivo tests indicated reduction of cytogenotoxic potential in the tested drinking water samples. The results support the potential applications of practically feasible in vivo biological test systems such as A. cepa root based tests and the fish erythrocyte based tests as complementary tools for screening cytogenotoxicity potential of the source water and water treatment waste reaching downstream of aquatic ecosystems and for evaluating cytogenotoxicity eliminating efficacy of the DWTPs in different seasons in view of human and ecological safety.

Combination of physico-chemical analysis, Allium cepa test system and Oreochromis niloticus erythrocyte based comet assay/nuclear abnormalities tests for cyto-genotoxicity assessments of treated effluents discharged from textile industries.

Bioassays for cyto-genotoxicity assessments are generally not required in current textile industry effluent discharge management regulations. The present study applied in vivo plant and fish based toxicity tests viz. Allium cepa test system and Oreochromis niloticus erythrocyte based comet assay and nuclear abnormalities tests in combination with physico-chemical analysis for assessing potential cytotoxic/genotoxic impacts of treated textile industry effluents reaching a major river (Kelani River) in Sri Lanka. Of the treated effluents tested from two textile industries, color in the Textile industry 1 effluents occasionally and color, biochemical oxygen demand and chemical oxygen demand in the Textile industry 2 effluents frequently exceeded the specified Sri Lankan tolerance limits for discharge of industrial effluents into inland surface waters. Exposure of A. cepa bulbs to 100% and 12.5% treated effluents from both industries resulted in statistically significant root growth retardation, mito-depression, and induction of chromosomal abnormalities in root meristematic cells in comparison to the dilution water in all cases demonstrating cyto-genotoxicity associated with the treated effluents. Exposure of O. niloticus to the 100% and 12.5% effluents, resulted in erythrocytic genetic damage as shown by elevated total comet scores and induction of nuclear abnormalities confirming the genotoxicity of the treated effluents even with 1:8 dilution. The results provide strong scientific evidence for the crucial necessity of incorporating cyto-genotoxicity impact assessment tools in textile industry effluent management regulations considering human health and ecological health of the receiving water course under chronic exposure.

Efficacy of Allium cepa test system for screening cytotoxicity and genotoxicity of industrial effluents originated from different industrial activities.

Efficacy of Allium cepa test system for screening cytotoxicity and genotoxicity of treated effluents originated from four types of industrial activities (two textile industries, three rubber based industries, two common treatment plants of industrial zones, and two water treatment plants) was assessed. Physico-chemical parameters including the heavy metal/metalloid levels of the effluents varied depending on the industry profile, but most of the measured parameters in the effluents were within the specified tolerance limits of Sri Lankan environmental regulations for discharge of industrial effluents into inland surface waters. In the A. cepa test system, the undiluted effluents induced statistically significant root growth retardation, mitosis depression, and chromosomal aberrations in root meristematic cells in most cases in comparison to the dilution water and upstream water signifying effluent induced cytotoxicity and genotoxicity. Ethyl methane sulphonate (a mutagen, positive control) and all the effluents under 1:8 dilution significantly induced total chromosomal aberrations in root meristematic cells in comparison to the dilution water and upstream water indicating inadequacy of expected 1:8 dilutions in the receiving waters for curtailing genotoxic impacts. The results support the use of a practically feasible A. cepa test system for rapid screening of cytotoxicity and genotoxicity of diverse industrial effluents discharging into inland surface waters.

Assessing toxicity of copper, cadmium and chromium levels relevant to discharge limits of industrial effluents into inland surface waters using common onion, Allium cepa bioassay.

Toxicity of copper, cadmium and chromium relevant to established tolerance limits for the discharge of industrial effluents into inland surface waters was evaluated by Allium cepa bioassay. The roots of A. cepa bulbs exposed to Cu(2+) (3 mg L(-1)) individually or in mixtures with Cd(2+) (0.1 mg L(-1)) or/and Cr(6+) (0.1 mg L(-1)) exhibited the highest growth inhibition, mitotic index depression and nuclear abnormalities. Root tip cells exposed to Cr(6+) or Cd(2+) alone or in mixture displayed significant chromosomal aberrations in comparison to the controls. EC50s for root growth inhibition followed the order Cu(2+) < Cd(2+) < Cr(6+) indicating greater toxicity of copper. The results show that the industrial effluent discharge regulatory limits for these metals need to be reviewed considering potential cyto-genotoxicity to biological systems.

Modulation of ethoxyresorufin O-deethylase and glutathione S-transferase activities in Nile tilapia (Oreochromis niloticus) by polycyclic aromatic hydrocarbons containing two to four rings: implications in biomonitoring aquatic pollution.

Despite ubiquity of polycyclic aromatic hydrocarbons (PAHs) in the tropical environments, little information is available concerning responses of tropical fish to PAHs and associated toxicity. In the present study, effects of five PAHs containing two to four aromatic rings on hepatic CYP1A dependent ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST) and serum sorbitol dehydrogenase (SDH) activities in Nile tilapia, a potential fish species for biomonitoring pollution in tropical waters, were evaluated. Results showed that EROD activities were induced by the PAHs containing four aromatic rings (pyrene and chrysene) in a dose dependent manner. However PAHs with two to three aromatic rings (naphthalene, phenanthrene and fluoranthene) caused no effect or inhibition of EROD activities depending on the dose and the duration. Fluoranthene was the most potent inhibitor. SDH results demonstrated that high doses of fluoranthene induced hepatic damage. GST activity was induced by the lowest dose of phenanthrene, fluoranthene and chrysene but high doses had no effect. The results indicate that induction of EROD enzyme in Nile tilapia is a useful biomarker of exposure to PAHs such as pyrene and chrysene. However EROD inhibiting PAHs such as fluoranthene in the natural environment may modulate the EROD inducing potential of other PAHs thereby influencing PAH exposure assessments.