## 1 Introduction  
The increasing of anthropogenic activities since the pre-industrial era produced a series of changes in the ecosystems due to the CO\({}_{2}\) increase in the atmosphere and high anthropogenic emissions such as the use of fossil fuel, electric power plants, and automobiles, among others [1]. Previous studies estimated that CO\({}_{2}\) concentrations in the atmosphere have been raised from 280 ppm, dated in the pre-industrial era, to current concentrations higher than 415 ppm (Mauna Loa-Hawaii-observatory 2021 [2]). In this way, mitigation strategies to combat the impact caused from the increase of greenhouse gases (such as carbon dioxide) and the climate change phenomena have been considered in the last few years [3]. Among the strategies to reduce the CO\({}_{2}\) atmosphere levels, some consist of large-scale carbon capture and storage (CCS) in geological formations, which might contribute to a 19% reduction of CO\({}_{2}\) emissions by 2050 [4]. However, despite of this current practice, there are some gaps in the environmental risk assessment of the technique;it still remains largely unexplored hampered by complex ecological relationships and different ecosystems [5,6].  
Many studies have been performed in the last few years in order to analyze the potential effects from CO\({}_{2}\) enrichment in the ocean caused by both increases in CO\({}_{2}\) atmosphere concentrations and natural uptake on seawater surface, and by CO\({}_{2}\) leakages during the CCS process (e.g., [7, 8, 9, 10]), as well as in combination with harmful substances [11,12].  
On the other hand, the weight-of-evidence (WoE) approach has been indicated as a good method to achieve precise results of environmental characterization and quality status [6, 13, 14, 15, 16]. According to [17], several questions commonly asked in an environmental assessment of chemicals include the following: Are contaminants present in the ecosystem and at what levels? Are contaminants bioavailable? Do they cause biological adverse effects? These questions were adapted in this study in relation to the influence of acidification caused by CO\({}_{2}\) enrichment in the seawater. In this sense, these questions were addressed in the present study in the Bay of Santos with particular chemical characterization and its characteristic infauna.  
Recent studies have evaluated the relationship between decrease in seawater pH, adverse effects on marine organisms, and changes in the metal concentrations [7, 8, 18, 19, 20, 21, 22, 23]. However, none of these studies have been designed or applied under an integrative point of view using multiples lines of evidence as recommended by [24].  
Therefore, the use of an integrated approach using the maximum amount of information could be an effective way to contribute with the studies of environmental risk related to CO\({}_{2}\) enrichment in the ocean, which would support stakeholders and policymakers in finding appropriate solutions for the conservation and protection of marine ecosystems. In the present study, the relationship between CO\({}_{2}\) enrichment in the ocean and increases of the contamination levels was assessed based on the WoE and using sediment and water physicochemical analysis, ecotoxicological analysis, and macro-benthic community alteration as the mains lines of evidence linked in the WoE.