Environmental monitoring and risk assessment in a tropical Costa Rican catchment under the influence of melon and watermelon crop pesticides.

A monitoring network was established in streams within a catchment near the Costa Rican Pacific coast (2008-2011) to estimate the impact of pesticides in surface water (84 samples) and sediments (84 samples) in areas under the influence of melon and watermelon production. A total of 66 (water) and 47 (sediment) pesticides were analyzed, and an environmental risk assessment (ERA) was performed for four taxa (algae, Daphnia magna, fish and Chironomus riparius). One fungicide and seven insecticides were detected in water and/or sediment; the fungicide azoxystrobin (water) and the insecticide cypermethrin (sediments) were the most frequently detected pesticides. The insecticides endosulfan (5.76 µg/L) and cypermethrin (301 µg/kg) presented the highest concentrations in water and sediment, respectively. The ERA revealed acute risk in half of the sampling points of the melon-influenced area and in every sampling point from the watermelon-influenced area. Safety levels were exceeded within and around the crop fields, suggesting that agrochemical contamination was distributed along the catchment, with potential influence of nearby crops. Acute risk was caused by the insecticides chlorpyrifos, cypermethrin and endosulfan to D. magna, fish and C. riparius; the latter was the organism with the overall highest/continuous risk. High chronic risk was determined in all but one sampling point, and revealed a higher number of pesticides of concern. Cypermethrin was the only pesticide to pose chronic risk for all benchmark organisms. The results provide new information on the risk that tropical crops pose to aquatic ecosystems, and highlight the importance of including the analysis of sediment concentrations and chronic exposure in ERA.

Amendments with pyrolyzed agrowastes change bromacil and diuron's sorption and persistence in a tropical soil without modifying their environmental risk.

Knowledge of pesticides fate in tropical soils and how it could be affected by pyrolyzed biomass as amendment is limited. Combining conventional and radiotracer methods, as well as risk assessment tools, the effects of several charred agrowastes on the sorption, persistence, and ecological risk of the herbicides bromacil (BMC) and diuron (DRN) were evaluated in a tropical agricultural soil under laboratory conditions. Pineapple stubble (PS), palm oil fiber (PF), and coffee hull (CH) were charred at 300 (torrefied) and 600 °C (biochar) and applied to the soil at 10 and 20 t ha-1 rates. The sorption coefficients (Koc) in unamended soil for BMC and DRN were 18.4 and 212.1 L kg-1, respectively. The addition of torrefied PS and PF caused a 3 to 4-fold increment in BMC sorption and a 3 to 6-fold change in DRN's sorption. The only biochar that affected the sorption was PS that increased DRN's sorption 3.5 times. The application of coffee hull materials had no significant effect. In terms of degradation (half-life, DT50), for unamended soil BMC's degradation (300 days) was limited compared to DRN (73 days). Alternatively, biodegradation (mineralization half-life time, MT50) was 1278 d for BMC and 538 for DRN. While only PF and CH torrefied increased BMC's persistence, all the torrefied affected DRN's persistence. However, despite the observed effects, the predicted ecological risk was not mitigated. Our results highlight the need for scientific evidence on the use of pyrolyzed organic amendments to assess potential benefits and prevent unintended impacts in tropical agroecosystems.

Pesticide monitoring and ecotoxicological risk assessment in surface water bodies and sediments of a tropical agro-ecosystem.

A pesticide monitoring study including 80 and 60 active ingredients (in surface waters and sediments, respectively) was carried out in a river basin in Costa Rica during 2007-2012. A special emphasis was given on the exceptional ecological conditions of the tropical agro-ecosystem and the pesticide application strategies in order to establish a reliable monitoring network. A total of 135 water samples and 129 sediment samples were collected and analyzed. Long-term aquatic ecotoxicological risk assessment based on risk quotient in three trophic levels was conducted. Short-term risk assessment was used to calculate the toxic unit and prioritization of sampling sites was conducted by the sum of toxic units in both aquatic and sediment compartments. Dimethoate (61.2 µg/L), propanil (30.6 µg/L), diuron (22.8 µg/L) and terbutryn (4.8 µg/L) were detected at the highest concentrations in water samples. Carbendazim and endosulfan were the most frequently detected pesticides in water and sediment samples, respectively. Triazophos (491 µg/kg), cypermethrin (71.5 µg/kg), permethrin (47.8 µg/kg), terbutryn (38.7 µg/kg), chlorpyrifos (18.2 µg/kg) and diuron (11.75 µg/kg) were detected at the highest concentrations in sediment samples. The pesticides carbendazim, diuron, endosulfan, epoxyconazole, propanil, triazophos and terbutryn showed non-acceptable risk even when a conservative scenario was considered. Sum TUsite higher than 1 was found for one and two sampling sites in water and sediment compartments, respectively, suggesting high acute toxicity for the ecosystem. MAIN FINDING OF THE WORK: Exceptional ecological conditions of the tropical agro-ecosystem affect the fate of pesticides in water and sediment environment differently than the temperate one.