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Spatial and temporal evaluation of the urban runoff water flowing into recreational areas of Guarujá, São Paulo State, Brazil

ABSTRACT This study evaluated the water quality of the urban runoff flowing into the public beaches and recreational waters of Guarujá, São Paulo State, Brazil. Monthly samples were obtained from October 2017 to August 2018 in four beaches: Tombo (Blue Flag certification), Enseada (high-used by tourist), Perequê (fishing community) and Iporanga (conservation unit). Twenty-eight environmental variables (physical, chemical and microbiological) were analysed using standard statistical tests, and different quality indexes were obtained. Data showed that urban drainage channels are the main responsible for pollutant transport to the Guarujá Sea, mainly during the rainy season. Moreover, the different occupations and land uses appear to interfere with the water quality of the urban runoff. The best water quality was recorded at Iporanga (environmental compliance over 90% according to the Brazilian law, with low total phosphorus enrichment, but medium aluminium toxicity). The quality ratings for the other beaches were classified as very bad (57%–66% compliance with current legislation). Moreover, these waters were eutrophic showing high aluminium toxicity. This study highlights the environmental and public health risks arising from the urban runoff flowing into the beaches of Guarujá. Better water management practices, improvement of basic sanitation and population awareness, is highly recommended to prevent potential socio-environmental risks in this tourist area.