In this study, a weather-based multicomponent model was developed based on the unique biostructures and metabolic processes of mushrooms to evaluate their uptake of pesticides from soils, and the effects of temperature and relative humidity on the bioaccumulation of pesticides in mushrooms was comprehensively quantified. Additionally, a new pseudo-partition coefficient between mushrooms and soils was introduced to assess the impacts of different physiochemical properties on the pesticide uptake process. The results indicate that, in general, the pseudo-partition coefficient increases as the relative humidity increases for both the air and soil according to Fick’s law of gas diffusion and the spatial competition of molecules, respectively. Meanwhile, the effect of temperature on the pesticide bioaccumulation process is more complex. For most pesticides (e.g., atrazine), the pseudo-partition coefficient that was computed from the transpiration component had a maximum value at a specific temperature due to the temperature dependency of the transpiration and biodegradation processes. For some pesticides (e.g., ethoprophos), the pseudo-partition coefficient of the air-deposition component had a maximum value at a certain temperature that was caused by the ratio of the soil–air internal transfer energy and degradation activation energy of the pesticide. It was also concluded that for relatively low-volatility pesticides, transpiration dominated the bioaccumulation process; this was mainly determined from the pesticide water solubility. For nonbiodegradable pesticides (e.g., lindane), the computed coefficient values were relatively low due to their insolubility in water, which inhibits bioaccumulation in mushrooms and is one of the main reasons for their long-term persistence in soils.

Costa Rica is a tropical country with one of the highest biodiversity on Earth. It also has an intensive agriculture, and pesticide runoff from banana and pineapple plantations may cause a high toxicity risk to non-target species in rivers downstream the plantations. We performed a first tier risk assessment of the maximum measured concentrations of 32 pesticides detected over 4 years in the River Madre de Dios (RMD) and its coastal lagoon on the Caribbean coast of Costa Rica. Species sensitivity distributions (SSDs) were plotted in order to derive HC₅ values for each pesticide, i.e., hazard concentrations for 5 % of the species, often used as environmental criteria values in other countries. We also carried out toxicity tests for selected pesticides with native Costa Rican species in order to calculate risk coefficients according to national guidelines in Costa Rica. The concentrations of herbicides diuron and ametryn and insecticides carbofuran, diazinon, and ethoprophos exceeded either the HC₅ value or the lower limit of its 90 % confidence interval suggesting toxic risks above accepted levels. Risk coefficients of diuron and carbofuran derived using local guidelines indicate toxicity risks as well. The assessed fungicides did not present acute toxic risks according to our analysis. Overall, these results show a possible toxicity of detected pesticides to aquatic organisms and provide a comparison of Costa Rican national guidelines with more refined methods for risk assessment based on SSDs. Further higher tier risk assessments of pesticides in this watershed are also necessary in order to consider pesticide water concentrations over time, toxicity from pesticide mixtures, and eventual effects on ecosystem functions.

This study assesses the ecological risks (ERA) of pesticides to aquatic organisms in the River Madre de Dios (RMD), which receives surface runoff water from banana, pineapple, and rice plantations on the Caribbean coast of Costa Rica. Water samples collected over 2 years at five sites in the RMD revealed a total of 26 pesticides. Their toxicity risk to aquatic organisms was assessed using three recent ERA models. (1) The PERPEST model showed a high probability (>50 %) of clear toxic effects of pesticide mixtures on algae, macrophytes, zooplankton, macroinvertebrates, and community metabolism and a low probability (<50 %) of clear effects on fish. (2) Species sensitivity distributions (SSD) showed a moderate to high risk of three herbicides: ametryn, bromacil, diuron and four insecticides: carbaryl, diazinon, ethoprophos, terbufos. (3) The multi-substance potentially affected fraction (msPAF) model showed results consistent with PERPEST: high risk to algae (maximum msPAF: 73 %), aquatic plants (61 %), and arthropods (25 %) and low risk to fish (0.2 %) from pesticide mixtures. The pesticides posing the highest risks according to msPAF and that should be substituted with less toxic substances were the herbicides ametryn, diuron, the insecticides carbaryl, chlorpyrifos, diazinon, ethoprophos, and the fungicide difenoconazole. Ecological risks were highest near the plantations and decreased progressively further downstream. The risk to fish was found to be relatively low in these models, but water samples were not collected during fish kill events and some highly toxic pesticides known to be used were not analyzed for in this study. Further sampling and analysis of water samples is needed to determine toxicity risks to fish during peaks of pesticide mixture concentrations. The msPAF model, which estimates the ecological risks of mixtures based on their toxic modes of action, was found to be the most suitable model to assess toxicity risks to aquatic organisms in the RMD. The PERPEST model was found to be a strong tool for screening risk assessments. The SSD approach is useful in deriving water quality criteria for specific pesticides. This study, through the application of three ERA models, clearly shows that pesticides used in plantations within the RMD watershed are expected to have severe adverse effects on most groups of aquatic organisms and that actions are urgently needed to reduce pesticide pollution in this high biodiversity ecosystem.

Degradation and mineralization behavior of selected nematicides was studied in soil samples from fields cultivated with banana, potato, and coffee. Degradation assays in most of the studied soils revealed shorter half-lives for carbofuran (CBF) and ethoprophos (ETP) in samples with a history of treatment with these compounds, which may have been caused by enhanced biodegradation. A short half-life value for CBF degradation was also observed in a banana field with no previous exposure to this pesticide, but with a recent application of the carbamate insecticide oxamyl, which supports the hypothesis that preexposure to oxamyl may cause microbial adaptation towards degradation of CBF, an observation of a phenomenon not yet tested according to the literature reviewed. Mineralization assays for CBF and terbufos (TBF) revealed that history of treatment with these nematicides did not cause higher mineralization rates in preexposed soils when compared to unexposed ones, except in the case of soils from coffee fields. Mineralization half-lives for soils unexposed to these pesticides were significantly shorter than most reports in the literature in the same conditions. Mineralization rates for soils with a previous exposure to these pesticides were also obtained, adding to the very few reports found. This paper contributes valuable data to the low number of reports dealing with pesticide fate in soils from tropical origin.