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Biodiversity is declining on a global scale. Especially tropical ecosystems, containing most of the planetary biodiversity, are at risk. Agricultural monocrop systems contribute to this decline as they replace original habitats and depend on extensive use of synthetic pesticides that impact ecosystems. In this review we use large-scale banana production for export purposes in Costa Rica as an example for pesticide impacts, as it is in production for over a century and uses pesticides extensively for more than fifty years. We summarise the research on pesticide exposure, effects and risks for aquatic and terrestrial environment, as well as for human health. We show that exposure to pesticides is high and relatively well-studied for aquatic systems and humans, but hardly any data are available for the terrestrial compartment including adjacent non target ecosystems such as rainforest fragments. Ecological effects are demonstrated on an organismic level for various aquatic species and processes but are not available at the population and community level. For human health studies exposure evaluation is crucial and recognised effects include various types of cancer and neurobiological dysfunctions particularly in children. With the many synthetic pesticides involved in banana production, the focus on insecticides, revealing highest aquatic risks, and partly herbicides should be extended to fungicides, which are applied aerially over larger areas. The risk assessment and regulation of pesticides so far relies on temperate models and test species and is therefore likely underestimating the risk of pesticide use in tropical ecosystems, with crops such as banana. We highlight further research approaches to improve risk assessment and, in parallel, urge to follow other strategies to reduce pesticides use and especially hazardous substances.

Pesticides are used throughout the tropics in large amounts to protect crops against pests and weeds. These chemicals may be lost to the aquatic environment and impair its ecological status and the water quality for human consumption. Despite intensive use of pesticides in many developing countries, the knowledge of pesticide levels in aquatic ecosystems is often very limited. In this study, we try to fill this gap for an horticultural catchment of 35.9 km2 in Costa Rica, which is intensively used by small-holder farming for potatoes and vegetable production. We continuously monitored pesticides in the Tapezco river during two consecutive rainy seasons with passive sampling systems and screened for a broad set of polar and non-polar pesticides. Spatially distributed measurements revealed high pesticide concentrations of many fungicides, herbicides and insecticides throughout the watershed. Concentration ranges revealed little spatio-temporal variation. From an ecotoxicological point of view, the insecticide levels – notably chlorpyrifos and cypermethrin - were most critical. The observed concentration levels exceeded chronic environmental quality standards more than 100-fold at all sites. These high insecticide levels were partially reflected in the community composition of the macroinvertebrates. Available data revealed a poor status at two upstream locations according to the Costa Rican Biological Monitoring Working Party (BMWP-CR) Index and the SPEARpesticides index. However, the indices indicated a good quality at most downstream sites despite their high pesticide levels. The wide-spread occurrence of high pesticide levels demonstrated that the relevant sources and pathways existed throughout the catchment. Field observations and survey data showed the relevance of point sources due to poor pesticide handling as well as diffuse losses from fields, which are strongly enhanced by the steep terrain and linear structures like gullies connecting fields with the stream. Mitigation measures to reduce pesticide losses have to account for these different source-flowpath combinations.

The objective of this research was to determine the level of knowledge and perception of the Costa Rican population about water for human consumption, general concepts, the impact of human activities, the occurrence of extreme events and water management and governance. In 2016, a quantitative-descriptive study of population perception was carried out through a semi-structured survey in which 800 people were consulted, through calls to landlines. It was found that the Costa Ricans: a) perceived that water is a public good and that there is greater availability of water than there is in reality, b) 22 % indicated having supply problems, infrastructure and/or water quality, c) are aware of the contamination of water bodies and willing to pay more for the treatment of wastewater, d) perceived a negative impact due to floods and landslides and, e) 55 % agreed that water for consumption comes from wells and springs, but only 12 % and 36 % had a general notion of what an aquifer and groundwater is, respectively. It is concluded that education programs should include general concepts on groundwater, water management and governance and that the willingness to pay more for wastewater treatment should be taken into consideration by the institutions for the improvement of environmental sanitation.

The Volcán River watershed in the south Pacific of Costa Rica comprises forests, small urban settlements, cattle fields, and intensive agriculture (mostly pineapple and sugarcane). The ecological integrity and quality of its waters was assessed from 2011–2013 and 2018–2019 by means of physical–chemical parameters (pH, conductivity, temperature, DO, DBO, nitrate, total phosphorus, and pesticide residues) and benthic macroinvertebrate (MI) sampling in eight sites (Volcán, Cañas, and Ángel Rivers, and Peje and Maura streams), resulting in high ecological integrity in all sites except the Peje stream, which is polluted with nitrates and pesticides. Only in this stream was there a marked seasonal variation in the abundance of 16 MI families including Leptohyphidae, Leptophlebiidae, Philopotamidae, Glossossomatidae, and Corydalidae, among others, whose presence was limited exclusively to the dry season (December to April), disappearing from the stream in the rainy season, with corresponding peaks in nitrate (max 20.3 mg/L) and pesticides (mainly herbicides and organophosphate insecticides). The characteristics of the watershed, with large areas of forest and excellent water quality, allow for the re-colonization of organisms into the Peje stream; however, those organisms are incapable of development and growth, providing evidence of a contaminant-driven habitat fragmentation in this stream during the rainy season.

Neotropical ecosystems are highly biodiverse; however, the excessive use of pesticides has polluted freshwaters, with deleterious effects on aquatic biota. This study aims to analyze concentrations of active ingredients (a.i) of pesticides and the risks posed to freshwater Neotropical ecosystems. We compiled information from 1036 superficial water samples taken in Costa Rica between 2009 and 2019. We calculated the detection frequency for 85 a.i. and compared the concentrations with international regulations. The most frequently detected pesticides were diuron, ametryn, pyrimethanil, flutolanil, diazinon, azoxystrobin, buprofezin, and epoxiconazole, with presence in >20% of the samples. We observed 32 pesticides with concentrations that exceeded international regulations, and the ecological risk to aquatic biota (assessed using the multi-substance potentially affected fraction model (msPAF)) revealed that 5% and 13% of the samples from Costa Rica pose a high or moderate acute risk, especially to primary producers and arthropods. Other Neotropical countries are experiencing the same trend with high loads of pesticides and consequent high risk to aquatic ecosystems. This information is highly valuable for authorities dealing with prospective and retrospective risk assessments for regulatory decisions in tropical countries. At the same time, this study highlights the need for systematic pesticide residue monitoring of fresh waters in the Neotropical region.