DOI: 10.25678/0006ck
title: Risk assessment for tropical streams of a small-scale horticultural catchment based on spatio-temporal pesticide monitoring data

description: This package contains the supplementary information (SI) of chapter 3 of the dissertation of Frederik T. Weiss with the Dissertation No. ETH 27434 (defended: 24th February, 2021), entitled: "Pesticides in a tropical Costa Rican stream catchment: from monitoring and risk assessment to the identification of possible mitigation options".Generally within this thesis the supplementary information (SI) is divided into three parts (SI A, SI B, SI C). For each chapter, SI A section contains background information/data for the reader with quick and easy access added directly after each main chapter. SI B contains raw data, further processed data for analysis, and figures of processed data presented as Excel files. SI C combines the R scripts with information and commands utilized for the statistical analysis.The abstract of chapter 3 reads as follows:"A pesticide monitoring in the Tapezco river catchment region in two subsequent years (2015/2016) revealed that intensive pesticide use leads to contamination of streams. As shown in Chapter 2, 87 pesticide and pesticide transformation products (PPTP), comprising insecticides, herbicides, fungicides and several of their transformation products (TP) were identified by applying sorbent-based passive sampling approaches at the five (2015), respectively eight (2016), sub-catchment (SC) sites.Using these monitoring data as a basis, the first aim of this study was to exploit the measured environmental concentrations (MEC) of the PPTP with regard to their spatio-temporal distribution among the different sampling sites in the Tapezco river catchment. To enable a comparison between the two sampling years, of the 87 detected PPTP, the data set was narrowed down to those which were found in both sampling years, leading to a subset of 62 PPTP. Two MEC-based risk assessment approaches, one relying on Environmental Quality Standards (EQS) and the other on the Toxic Units (TU) concept focusing on invertebrates, were used to identify if the PPTP pose health risks to aquatic biota either singly or in mixture. As well, available macroinvertebrate data for four sites (SC1, SC4, SC5 and SC8) was evaluated in view of the indicated water quality, applying the species at risk pesticide (SPEARpesticide), the Costa Rican Biological Monitoring Working Party (BMWP-CR) Index, and the Ephemeroptera, Plecoptera and Tricoptera (EPT)-taxa richness indices.For the 62 considered PPTP, spatial trends were observed. In more detail, at two connected sites (SC2 and SC3), the average number of PPTP was 2-fold lower compared to the six remaining sites. At all sites, insecticides had the broadest detected spectrum as opposed to the numbers of individual herbicides and fungicides. Conversely, at all sites and periods, fungicides had the highest average %contribution of the average sum-concentration among the individual detected pesticide types. Independent of the risk assessment approach applied, the quality of the water was indicated to be generally poor, pointing at chronic, and even acute effects to be expected for aquatic communities at all sampling sites. Invertebrates were the most affected organism group based on EQS and TU without any apparent time window to recover from pesticide stress during both sampling years. The SPEARpesticide and the BMWP-CR indices both indicated that, despite the continuous pesticide pollution stress at all sites, water quality seemed to be improved at SC5 and reached even a good to regular water quality at the most downstream site (SC8) compared to the other remaining sites (SC1 and SC4) for which macroinvertebrate data was available. The EPT-taxa richness index showed as well an improvement in water quality at SC8. This finding could be due to a larger river stretch upstream to the sampling site with no horticultural land and high share of natural forest.Given that all applied approaches confirmed substantial risks, there is an urgent need for a reduction of pesticides in streams of the Tapezoco catchment to improve the water quality in order to protect aquatic communities in these streams."