Heavy Metal Threats to Plants and Soil Life in Southern Africa: Present Knowledge and Consequences for Ecological Risk Assessment

Ecotoxicological evaluation of surface waters in Northern Namibia

The increasing pressure on freshwater systems due to intensive anthropogenic use is a big challenge in central-northern Namibia and its catchment areas, the Kunene and the Kavango Rivers, and the Cuvelai-Etosha Basin, that provide water for more than 1 million people. So far, there is no comprehensive knowledge about the ecological status and only few knowledge about the water quality. Therefore, it is crucial to learn about the state of the ecosystem and the ecological effects of pollutants to ensure the safe use of these resources. The surface waters of the three systems were sampled, and three bioassays were applied on three trophic levels: algae, daphnia, and zebrafish embryos. Additionally, in vitro assays were performed to analyze mutagenicity (Ames fluctuation), dioxin-like potential (micro-EROD), and estrogenicity (YES) by mechanism-specific effects. The results show that acute toxicity to fish embryos and daphnia has mainly been detected at all sites in the three catchment areas. The systems differ significantly from each other, with the sites in the Iishana system showing the highest acute toxicity. At the cellular level, only weak effects were identified, although these were stronger in the Iishana system than in the two perennial systems. Algae growth was not inhibited, and no cytotoxic effects could be detected in any of the samples. Mutagenic effects and an estrogenic potential were detected at three sites in the Iishana system. These findings are critical in water resource management as the effects can adversely impact the health of aquatic ecosystems and the organisms within them.

Do Endemic Soil Fauna Species Deserve Extra Protection for Adverse Heavy Metal Conditions?

The concept of Ecotoxicological Species Sensitivity Distributions, as used in EU and US, to derive environmental standards for contaminants, starts from the assumption that by protecting the majority of species (95% confidence interval) all species will be protected. Nevertheless, 5% of the species outside the confidence interval might become harmed; half of it being the most sensitive for the particular compound tested. With respect to protection of rare endemic species it is not clear, however, if contamination is a driving factor for endemicity. The aim of this paper is to explore whether endemic and rare species deserve extra protection from adverse environmental conditions. To this end, a brief overview of the various forms of endemism, their relation to environmental stress factors and the distribution of endemic species is discussed. Further, the sensitivities of these species towards environmental stress factors are analysed, in order to conclude if and how endemic species could be better protected against environmental stress factors. This was achieved by specifically focusing on the potential impacts of metalliferous soils, mining, the treatment of mined soil and the storage of treated mine waste. It is concluded that at present there are some signals about specific sensitivities, but the database is much too small for a definite conclusion about adverse environmental factors as a threat to endemic species. The data gap has to be filled in with experimental tests with endemic species. This is hampered by the protection status of these endemic, rare species. Recommendations and derived activities are proposed to address this.

Colorimetric Detection Based on Localized Surface Plasmon Resonance Optical Characteristics for Sensing of Mercury Using Green-Synthesized Silver Nanoparticles

Development of selective colorimetric detectors that can use green-fabricated silver nanoparticles' (AgNPs) with localized surface plasmon resonances (LSPRs) to rapidly, simply, and selectively detect Hg(II) ions was undertaken in this study. Onion extract was used for synthesising photo-induced green crystalline silver nanoparticles (NPs). The formation of nanoparticles is enhanced when ultrasound irradiation is present; bioligands could serve as stabilizing and reducing agents. Different methods of measurement, including UV-Vis, TEM, SEM/EDAX, FT - IR, and XRD, are effective for characterization of nanoparticles. The spherical nature of green-fabricated AgNPs is confirmed by TEM. High-density, spherical, and uniformly formed silver nanoparticle shapes were found in silver nanoparticle SEM images. The arrangement of AgNPs in the form of face-centered cubic structures was confirmed by XRD patterns. The formation of impurity-free AgNPs was confirmed using the EDAX analysis results. Hg2+ with excellent sensitivity was sensitively and selectively detected by employing green-synthesized silver nanoparticles. The reduction of Ag (1) to Ag (0) was confirmed by a slight increase in Hg (II) concentration and progressive reduction of green-synthesized AgNPs, whose absorbance changed abruptly. The reduction of LSPRs by the phosphate buffer medium enables AgNPs to sensitively and selectively detect Hg2+ ions by providing good environment. Besides, a selective, sensitive, simple, and rapid method that is proposed for detecting Hg (II) ions in samples of water is presented in the study. Harmful mercury ions in real samples of water (tap and ground water) can colorimetrically and selectively be detected using the AgNPs. The results showed an RSD of below 6% and over 92% of good recovery.