Temporal Evolution of Emerging Contaminants, Priority Substances and Heavy Metals Most Frequently Detected in Reclaimed Water and Groundwater in a Volcanic Aquifer

EXTENDED ABSTRACT The presence of emerging contaminants has been previously described in reclaimed water and groundwater of Gran Canaria (Spain). Despite of the environmental risk associated to irrigation with reclaimed water (R), this practice is necessary considering sustainability of the hydrological cycle in semiarid zones, especially regarding agricultural activity. The aim of this study was: i) to analyse the evolution during two years of contaminants of emerging concern, priority substances (2008/105/EC) and heavy metals in reclaimed water (R) and in a volcanic aquifer in the NE of Gran Canaria where a golf course has been irrigated with R since 1976 and ii) to relate this presence with physicochemical water properties and hydrogeological media. Reclaimed water and groundwater (GW) were monitoring quarterly from July 2009 to September 2011. Sorption and degradation processes in soil account for more compounds being detected in R. Diazinon and chlorfenvinphos were detected always in R and terbuthylazine, terbutryn and diuron at 90% of frequency. Considering all the samples, the most frequent compounds were chlorpyrifos ethyl, fluorene, phenanthrene and pyrene. Although their concentrations were frequently below 50 ngL, some contaminants, such as chlorpyrifos ethyl, were occasionally detected at higher concentrations. This priority substance for surface water exceeded the maximum threshold (0.1 μgL) for pesticide concentration in groundwater (2006/118/EC). The high frequency and concentration of this adsorbable compound are consistent with the preferential flow described in volcanic aquifers. In this sense, the highest values obtained in groundwater coincided with high EC or nitrate contents, and were localized in one well. Geology and location seem to be related to the emerging compounds presence due to occasional contamination events (not related to R irrigation) and therefore not to an existence of a dangerous diffuse contamination level. Thus, it is preferable to select wells with less stable chemical water quality, in order to monitor the risk of emerging compounds presence. Furthermore, the organochlorine insecticide and acaricide, alpha endosulfan, was detected once in four samples, above the threshold limit. Considering the relationship between contaminant presence, chemical water quality, seasonal variation, hydrogeological characteristics and wells location we can conclude that chlorpyrifos ethyl and alpha endosulfan were the most dangerous priority substances in terms of GW quality so they must be included in all of the monitoring studies, at least in Canary Islands.