Brazilian soil conditions in ecotoxicological tests: do international protocols represent the reality?

Abstract

This brief communication analyzes five critical aspects of soil ecotoxicological testing protocols and their applicability to tropical and subtropical conditions, particularly in Brazil: tropical artificial soil (TAS) composition, natural soil variability, pH dynamics, organic matter content, and soil clay mineralogy. While standardized artificial soil testing has been fundamental for generating comparable data across regions, significant differences exist between TAS and natural Brazilian soils. Standard artificial soil, as specified in ecotoxicity protocols, contains 10% organic matter and has a pH of 6.0 ± 0.5, whereas natural soils typically contain 1.5–3.0% organic matter and are more acidic (pH 4.8–5.6). Additionally, while TAS primarily contains kaolinite clay and quartz, many natural soils are also characterized by iron oxides and gibbsite, which significantly influence contaminant retention and bioavailability. The TAS adaptation, using coconut husk fiber instead of peat moss, represents an improvement but still may not fully reflect local conditions. Brazil’s extensive pedo-mineralogical diversity presents important challenges for establishing representative ecotoxicological testing conditions and validity criteria based on natural soils. These differences can significantly affect contaminant mobility, bioavailability, and toxicity, potentially leading to different outcomes compared with standardized artificial soil tests. This analysis highlights the need for future methodological and regulatory discussions aimed at improving the environmental representativeness of tropical soil ecotoxicology while preserving the benefits of standardization. A promising perspective involves the development of tiered testing frameworks that combine standardized artificial soils for screening and inter-laboratory harmonization with representative natural tropical soils for higher-tier ecological assessments. Such approaches could enhance the ecological realism of risk assessments by integrating biological responses with key physicochemical and mineralogical soil characteristics, ultimately supporting more robust and regionally relevant ecotoxicological evaluations in tropical and subtropical regions.