Se determinaron las concentraciones de Arsénico (As) presentes en muestras de agua para uso y consumo humano recolectadas en 106 operadores comunales de sistemas de abastecimiento en las regiones Chorotega y Huetar Norte de Costa Rica durante 2013-2017. A las muestras que registraron concentraciones de As por encima de la norma nacional se le evaluaron los restantes parámetros incluidos en el nivel N2 del Reglamento para agua potable de Costa Rica. La determinación de arsénico se hizo utilizando espectrometría de absorción atómica con horno de grafito. Los principales incumplimientos se registraron en los distritos de Bagaces y Cañas mientras que en la Región Huetar Norte se presentan en Agua Zarcas y Los Chiles. En estos distritos se registra un nivel de incumplimiento de la norma nacional (10 µg/l) que varía desde 66,7 % en el caso de Los Chiles hasta un 50 % en Cañas. Los sistemas que presentan incumplimientos no registraron variaciones temporales significativas en las concentraciones de As en el periodo 2013-2017. Al analizar los parámetros de correlaciones significativas registradas entre el As y las otras especies analizadas se obtiene información valiosa relacionada con los procesos hidrogeoquímicos que determinan la presencia de este metaloide.

A database was built with the results of the physicochemical analysis of 23,435 samples of wastewater discharges obtained from the operational reports presented and the cross-checks carried out by the Ministry of Health to the operating entities, in accordance with the provisions of Decree 30661-MINAE-S, for the period 2016–2020. Using Bayesian networks, the probabilities of compliance with current regulations were estimated by preparing an acyclic directed graph for three alternative scenarios. At the national level, the BOD and the COD are the variables that record the lowest values, showing important differences between the results obtained for the central region of the country with respect to the other regions. Another determining variable turned out to be the type of final disposal, wherein the reuse of wastewater presents important compliance deficiencies for all regions except for Chorotega. In the case of BOD, COD and TSS, the lowest probabilities are recorded for ISIC codes 3821 (treatment of non-hazardous waste), 1040 (manufacture of animal and vegetable fats) and 145 (pig farming). Additionally, the integrated environmental risk was calculated as a product of the discharges, obtaining that for the evaluated parameters, the BOD and COD represent the highest risk values given their probability of occurrence rate, as well as the magnitude of the environmental impact. The Pacifico Central and Brunca regions recorded the highest integrated environmental risk value for BOD, COD and TSS compared to the other areas of the country. Based on the results obtained, proposals for improvement were generated for the control of wastewater discharges carried out by the environmental authorities in search of achieving a better comprehensive management of the water resource.

Chlorination is one of the most important stages in the treatment of drinking water due to its effectiveness in the inactivation of pathogenic organisms. However, the reaction between chlorine and natural organic matter (NOM) generates harmful disinfection by-products (DBPs), such as trihalomethanes (THMs). In this research, drinking water quality data was collected from the distribution networks of 19 rural and semi urban systems that use water sources as: springs, surfaces, and a mixture of both, in three provinces of the Paci c slope of Costa Rica during April 2018 to September 2019. Twelve models were developed from four data sets: all water sources, spring, surface, and mixture of spring and surface waters. Linear, logarithmic, and exponential multivariate regression models were developed for each data set to predict the concentration of total trihalomethanes (TTHMs) in the distribution networks. Concentrations of TTHMs were found between < 0.20 to 91.31 µg/L, with chloroform being the dominant species accounting for 62% of TTHMs on average. Turbidity, free residual chlorine, total organic carbon (TOC), dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV 254 ) showed a signi cant correlation with TTHMs. In all the data sets the linear models presented the best goodness-of-t and were moderately robust. Four models, the best of each data set, were validated with data from the same systems, and, according to the criteria of R 2 , SE, MSE and MAE, spring water and mixed spring/surface water models showed a satisfactory level of explanation of the variability of the data. Moreover, the models seem to better predict TTHMs concentrations below 30 µg/L. These models were satisfactory and could be useful for decision-making in drinking water supply systems and be considered in possible modi cations in current legislation. prediction in Costa Rica, and to the best of the authors knowledge in the Central American and Caribbean region. Furthermore, this study was focused in rural and semi urban areas, where no studies was found in the literature.In Costa Rica, 93% of the population received drinking water in 2019 (PEN and CONARE 2020). Moreover, in the same year, 19.4% of homes in rural and semi-urban areas were supplied with water by local Associations Administrators of Aqueduct and Sewerage Systems, (ASADAs in Spanish) (Sánchez-Hernández 2019). In addition, in 2016, 14.3% of the population was supplied by 24 municipalities and the rest by duly organized public companies (AyA 2016). The main water sources used are groundwater, springs, surface water and the mixture of the two latter ones, moreover, in all cases chlorine disinfection is the method used (Arellano-Hartig et al. 2020). In general, due to economic and analytical capacity limitations, monitoring of THMs is scarce, mainly at the ASADAs and municipal level. Thus, the objective of this study was to develop a series of prediction models of TTHMs in the distribution systems of rural and semi-urban areas supplied by springs, surface water and t...

Chlorination is one of the most important stages in the treatment of drinking water due to its effectiveness in the inactivation of pathogenic organisms. However, the reaction between chlorine and natural organic matter (NOM) generates harmful disinfection by-products (DBPs), such as trihalomethanes (THMs). In this research, drinking water quality data was collected from the distribution networks of 19 rural and semi urban systems that use water sources as: springs, surfaces, and a mixture of both, in three provinces of the Pacific slope of Costa Rica during April 2018 to September 2019. Twelve models were developed from four data sets: all water sources, spring, surface, and mixture of spring and surface waters. Linear, logarithmic, and exponential multivariate regression models were developed for each data set to predict the concentration of total trihalomethanes (TTHMs) in the distribution networks. Concentrations of TTHMs were found between < 0.20 to 91.31 µg/L, with chloroform being the dominant species accounting for 62% of TTHMs on average. Turbidity, free residual chlorine, total organic carbon (TOC), dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV254) showed a significant correlation with TTHMs. In all the data sets the linear models presented the best goodness-of-fit and were moderately robust. Four models, the best of each data set, were validated with data from the same systems, and, according to the criteria of R2, SE, MSE and MAE, spring water and mixed spring/surface water models showed a satisfactory level of explanation of the variability of the data. Moreover, the models seem to better predict TTHMs concentrations below 30 µg/L. These models were satisfactory and could be useful for decision-making in drinking water supply systems and be considered in possible modifications in current legislation.