Development of an ecotoxicological test procedure for soil microalgae.

Since the 80s, ISO and OECD organizations have been developing guidelines for assessing the toxicity of new and existing chemical substances to soil biota. Up to now, any of these guidelines had soil algae as test organisms. Nevertheless, microalgae are relevant components of soil microbial communities and soil biological crusts (BSC) with a great contribution to different soil functions and ecosystem services. In an attempt to bridge the gap, the present work aimed to develop, describe and validate a standard operating procedure for an ecotoxicological test with soil microalgae. Three phases were performed, each one with specific objectives. First, soil microalgae and cyanobacteria were isolated from BSC and then genetically and morphologically characterized. The green microalga Micractinium inermum was selected because it is a species with a wide geographic distribution. Secondly, M. inermum growth curves were obtained in liquid (BG11 and Woods-Hole MBL) and solid media (OECD artificial soil) to determine test duration. The growth curves were also used to analyze the reproducibility of the test's endpoint and to propose a validation criterion. Ultimately, a range of concentrations of two reference substances (glyphosate and copper) were tested, both in soil and liquid media, to assess procedure's reproducibility. The tests made in liquid medium followed the standard guideline for ecotoxicological tests with freshwater microalgae and cyanobacteria (OECD 201:2011). The results obtained prove that when the artificial soil is used, as a test substrate, the sensitivity of M. inermum increases. The tests performed with both reference substances demonstrate that the procedure described for testing in soil was reproducible. Additionally, it will be relevant to test with other reference substances and adjust the procedure for natural soils. It will be also interesting to validate the test procedure with soil cyanobacteria.

TiO2 nanoparticles for the remediation of eutrophic shallow freshwater systems: Efficiency and impacts on aquatic biota under a microcosm experiment.

The application of nanomaterials (NMs) in the remediation of eutrophic waters, particularly in the control of internal loading of nutrients, has been started, but limited investigations evaluated the effectiveness of these new treatment approaches and of their potential impacts on species from shallow freshwater lakes. The present work investigated, under a microcosm experiment, the application of a TiO2 nanomaterial both for reducing nutrient (mainly phosphorus and nitrogen forms) desorption and release from sediments (preventive treatment-PT) and for eliminating algal blooms (remediation treatment-RT). Furthermore, we also intended to assess the potential impacts of nano-TiO2 application on key freshwater species. The results showed the effectiveness of nano-TiO2 in controlling the release of phosphates from surface sediment and the subsequent reduction of total phosphorus in the water column. A reduction in total nitrogen was also observed. Such changes in nutrient dynamics contributed to a progressive inhibition of development of algae after the application of the NM in PT microcosms. Concerning the ability of nano-TiO2 to interact with algal cells, this interaction has likely occurred, mainly in RT, enhancing the formation of aggregates and their rapid settlement, thus reducing the algal bloom. Both treatments caused deleterious effects on freshwater species. In PT, Daphnia magna and Lemna minor showed a significant inhibition of several endpoints. Conversely, no inhibitory effect on the growth of Chironomus riparius was recorded. In opposite, C. riparius was the most affected species in RT microcosms. Such difference was probably caused by the formation of larger TiO2-algae aggregates in RT, under a high algal density, that rapidly settled in the sediment, becoming less available for pelagic species. In summary, despite the effectiveness of both treatments in controlling internal nutrient loading and in the mitigating algal bloom episodes, their negative effects on biota have to be seriously taken into account.