Antioxidant Response in Duckweed After Exposure to Secondary Effluent from Municipal Wastewater Treatment Plant, Elazığ, Turkey

Duckweed biomarkers for identifying toxic water contaminants?

Surface or ground waters can be contaminated with numerous toxic substances. The duckweeds Lemna minor and Lemna gibba are widely used for assaying waterborne toxicity to higher plants in terms of growth inhibition and photosynthetic pigment reduction. These tests cannot, however, in themselves determine the nature of the agents responsible for toxicity. Morphological, developmental, physiological, biochemical, and genetic responses of duckweeds to exposure to toxic water contaminants constitute biomarkers of toxic effect. In principle, the very detection of these biomarkers should enable the contaminants having elicited them (and being responsible for the toxicity) to be identified. However, in practice, this is severely compromised by insufficient specificity of biomarkers for their corresponding toxicants and by the lack of documentation of biomarker/toxin relationships. The present contribution illustrates the difficulties of using known water contaminant-related duckweed biomarkers to identify toxins, and discusses possibilities for achieving this goal.

Chronic Exposure to Water of Lake Qaroun Induced Metal-Related Testicular Damage and Endocrine Disruption in Male Fish

The uncontrolled releasing of hazardous wastes into Lake Qaroun was adversely impacting the aquatic environment and its biota. Therefore, this approach was designed to investigate the impact of these discharges on the reproductive and testicular function of Oreochromis niloticus. Several biomarkers were applied on the testicular tissues as metal bioaccumulation levels, histological examination with recording the ovotestis appearance and antioxidant status after 45 days of exposure to 0, 10, 20, & 30% of Lake Qaroun water (LQW). The bioaccumulated Cu, Mn, Fe, Pb, and Cd were unequally distributed in the testes but all these metals showed a significant concentration-dependent elevation among the studied groups. The exposure to LQW significantly increased the histological alterations in the testicular tissues as vacuolar degeneration, loss of tubular organization, and degeneration of Leydig cell. Based on the frequent appearance of histopathological abnormalities and ovotestis recording, the most deformed testicular tissues were observed in the 30% LQW-exposed groups. The ovotestis severity index (OSI) was significantly raised in LQW-exposed groups compared to the control group. The activities of superoxide dismutase, catalase as well as glutathione-reduced levels were significantly (p < 0.05) decreased in testes after chronic exposure to LQW. On the other pole, the activities of glutathione peroxidase enzyme and malondialdehyde formation were sharply increased. In view of the above, the exposure to LQW induced metal-related oxidative damage to the testicular tissues and impaired the male reproductive health. This study showed strong correlations between the anthropogenic activities around Lake Qaroun and the reproductive dysfunction in fish.

The Response of Duckweed (Lemna minor L.) Roots to Cd and Its Chemical Forms

The response of duckweed (Lemna minor L.) roots to Cd and its chemical forms was investigated. The relative root growth rate and concentrations of Cd and its different chemical forms in the root, that is, ethanol-extractable (FE-Cd), HCl-extractable (FHCl-Cd), and residual fractions (Fr-Cd), were quantified. Weibull model was used to unravel the regression between the relative root elongation (RRL) with chemical forms of Cd. Parameters assessed catalase (CAT), peroxidases (POD), and superoxide dismutase (SOD), as well as malondialdehyde (MDA) and total antioxidant capacity (A-TOC). Our results show that both the relative root growth rate and relative frond number were affected by Cd concentrations. The chemical forms of Cd were influenced by Cd content in the medium. Relative root elongation (RRL) showed a significant correlation with chemical forms of Cd. Additionally, POD and SOD increased at lower Cd concentrations followed by a decrease at higher Cd concentrations (at more than 5 μM Cd). Moreover, MDA and A-TOC increased and CAT decreased with increasing Cd exposure. Furthermore, CAT showed a significant correlation with FHCl-Cd. Taken together, it can be concluded that the chemical forms of Cd are statistically significant predictors of Cd toxicity to duckweed and to the other similar aquatic plants.