Abstract
Ecosystems are subject to various stress factors, such as temperature rises due to climate changes and metal disposal. Thermal stress can amplify or mask the effects of metals on aquatic organisms. This study aims to carry out a systematic review on the effects of temperature rises due to climate changes on the toxicity of metals for freshwater organisms. Searches were made in different electronic databases and article selection was based on the following inclusion criteria: concordance with the question of a systematic review; publication in English, Spanish, and Portuguese between 1960 and 2020; and the use of standard methodology. Forty-three articles were included, which were classified with respect to the year and country of publication, test-organisms and metals studied, temperatures tested, and the effects observed. In 80% of the studies analyzed, a temperature rise was responsible for increasing the toxicity of metals for the aquatic organisms. The temperatures studied contemplated the temperature rise predicted by the Intergovernmental Panel for Climate Change at the end of the 21st century. Brazil stood out among the countries for having the greatest number of research studies in this area, although there is still the need for an increase in studies in tropical climate regions. Based on the literature review, it was shown that the metals most studied were copper and cadmium and the test-organisms most used in the research projects were fish. The information obtained from ecotoxicological studies is essential to predict the effects and prevent the risks associated with the metal contamination of aquatic ecosystems due to climate changes.
Highlights
One important variable to be considered in aquatic ecosystems is the temperature, due to its importance in maintaining the species and the metabolism of the aquatic systems (Esteves, 2011)
The aquatic ecosystem biota is especially vulnerable to temperature variations since most of the species are ectothermic, that is, their body temperatures change with alterations in the environmental temperature (Hochachka and Somero, 2002) and temperature rises are associated with alterations in the distribution and a decline in the diversity of phytoplankton (Lenard et al, 2019), zooplankton (Adamczuk, 2016), and fish (Herrera-R et al, 2020) in freshwater systems
This systematic review showed that according to most of the studies concerning the effects of metals with temperature rises, there was an increase in toxicity for microalgae, zooplankton, and fish species
Summary
One important variable to be considered in aquatic ecosystems is the temperature, due to its importance in maintaining the species and the metabolism of the aquatic systems (Esteves, 2011). Deforestation of the riparian forest, the construction of reservoirs, canalization of aquatic bodies, and the disposal of hot water used in the refrigeration processes of refineries, steel mills, and thermoelectric plants are related to the temperature rise of aquatic systems (Qiu, 2012; Raptis et al, 2016). Temperature rises and the entrance of pollutants are considered stressors that affect the occurrence of species in the ecosystems (Noyes and Lema, 2015; Gill et al, 2020). Freshwater ecosystems are more sensitive to climate change due to the temperature rise and changes in the precipitation patterns and water flow (Da Silva et al, 2020)
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