The use of pesticides in households and peri-urban areas of the Amazon has increased notably during the last years. Yet, the presence of these contaminants in Amazonian freshwater ecosystems remains unexplored. Here, we assessed the exposure to 18 pesticides and 5 transformation products in the Amazon River and in the urban streams of Manaus, Santarém, Macapá, and Belém (Brazil). Pesticide concentrations were analyzed by liquid and gas chromatography methods. Ecological risks were assessed following a two-tiered approach. First, hazard quotients and an overall hazard index were calculated using toxicity data for standard test species of primary producers, invertebrates, and fish. Second, the pesticides showing moderate-to-high ecological risks in the first tier were evaluated using Species Sensitivity Distributions (SSDs). Our study shows that pesticides are widespread in urban and peri-urban areas of the Brazilian Amazon. The frequency of detection was higher in urban streams than in the Amazon River, with some samples taken in Manaus, Santarém, and Belém containing up to 8 compounds. Most pesticides were measured at relatively low concentrations (ng L^-1), except for malathion, carbendazim and the bulk concentration of chlorpyrifos, which were monitored at concentrations above 100 ng L^-1. Based on the first-tier assessment, we found moderate-to-high risks for freshwater invertebrates for malathion, chlorpyrifos, and chlorpyrifos-methyl, and moderate risks for malathion to fish. The risk assessment performed with SSDs indicated high risks of malathion and chlorpyrifos-methyl in urban areas, with up to 15% and 5% of invertebrate species potentially affected, respectively. The bulk concentrations of chlorpyrifos resulted in high risks in some urban areas (14-22% of species affected) and in areas of the main river (32-44%) impacted by agriculture. We conclude that pesticide residues may contribute to a biodiversity impact in the Amazon and should be further monitored in urban and peri-urban areas, particularly after heavy rainfall events.

Nanoplastics (NPs) are particles ranging in size between 1 and 1000 nm, and they are a form of environmental contaminant of great ecotoxicological concern. Although NPs are widespread across ecosystems, they have only recently garnered growing attention from both the scientific community and regulatory bodies. The present study reviews scientific literature related to the exposure and effects of NPs and identifies research gaps that impede the finalization of related environmental risk assessments (ERAs). Approximately 80 articles published between 2012 and 2021 were considered. Very few studies (eight articles) focused on the presence of NPs in biotic matrices, whereas the majority of the studies (62 articles) assessed the lethal and sublethal effects of NPs on aquatic and terrestrial organisms. Whilst many studies focused on nude NPs, only a few considered their association with different aggregates. Amongst NPs, the effects of polystyrene are the most extensively reported to date. Moreover, the effects of NPs on aquatic organisms are better characterized than those on terrestrial organisms. NP concentrations detected in water were close to or even higher than the sublethal levels for organisms. An ERA framework specifically tailored to NPs is proposed.

Tire particles (TPs) are one of the main emission sources of micro- and nano-plastics into the environment. Although most TPs are deposited in the soil or in the sediments of freshwater and although they have been demonstrated to accumulate in organisms, most research has focused on the toxicity of leachate, neglecting the potential effects of particles and their ecotoxicological impact on the environment. In addition, studies have focused on the impact on aquatic systems and there are many gaps in the biological and ecotoxicological information on the possible harmful effects of the particles on edaphic fauna, despite the soil ecosystem becoming a large plastic sink. The aim of the present study is to review the environmental contamination of TPs, paying particular attention to the composition and degradation of tires (I), transport and deposition in different environments, especially in soil (II), the toxicological effects on edaphic fauna (III), potential markers and detection in environmental samples for monitoring (IV), preliminary risk characterization, using Forlanini Urban Park, Milan (Italy), as an example of an urban park (V), and risk mitigation measures as possible future proposals for sustainability (VI).

The species sensitivity distribution (SSD) calculates the hazardous concentration at which 5% of species (HC₅) will be potentially affected. For many compounds, HC₅ values are unavailable impeding the derivation of SSD curves. Through a detailed bibliographic survey, we selected HC₅ values (from acute toxicity tests) for freshwater aquatic species and 129 pesticides. The statistical distribution and variability of the HC₅ values within the chemical classes were evaluated. Insecticides are the most toxic compounds in the aquatic communities (HC₅ = 1.4 × 10⁻³ µmol L⁻¹), followed by herbicides (HC₅ = 3.3 × 10⁻² µmol L⁻¹) and fungicides (HC₅ = 7.8 µmol L⁻¹). Subsequently, the specificity of the mode of action (MoA) of pesticides on freshwater aquatic communities was investigated by calculating the ratio between the estimated baseline toxicity for aquatic communities and the HC₅ experimental values gathered from the literature. Moreover, we proposed and validated a scheme to derive the ecological thresholds of toxicological concern (eco-TTC) of pesticides for which data on their effects on aquatic communities are not available. We proposed eco-TTCs for different classes of insecticides, herbicides, and fungicides with a specific MoA, and three eco-TTCs for those chemicals with unavailable MoA. We consider the proposed approach and eco-TTC values useful for risk management purposes.

Climate change is increasing flash flood frequency and intensity around the globe, which can contribute to the mobilization of urban and agricultural contaminants into aquatic ecosystems. In October 2024, a massive flash flood affected the Valencia region (Spain), which discharged contaminated water into the Albufera Natural Park (ANP), a protected Mediterranean wetland. In this study we provide one of the most comprehensive assessments to characterize the contamination footprint produced by a flash flood event in downstream aquatic ecosystems. We evaluated physical-chemical parameters, pathogenic bacteria, and 241 organic contaminants, including pesticides (PEST), pharmaceuticals and personal care products (PPCPs), perfluoroalkyl substances (PFAS), organophosphorus flame retardants (OPFRs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs), in 15 sampling sites along the ANP. Our study reveals an increase of pathogenic bacteria and chemical exposure concentrations in the north-west areas of the ANP, correlating with elevated ammonia and reduced oxygen levels. Comparison with pre-flood data revealed significant concentration increases for PPCPs, PFAS, PAHs, and OPFRs, attributed to wastewater treatment failures and urban/industrial chemical mobilization. Several pollutants were found to significantly exceed established ecological protection thresholds (risk quotients > 10), with the most significant risks identified for ibuprofen, PFOS, and fluoranthene in water samples, along with 13 sediment-associated contaminants (including PFOS and several PESTs and PPCPs). This study provides a basis for guiding future monitoring and interventions designed to assess and prevent contamination risks from flash floods in freshwater ecosystems.