Investigating the relationship between nitrate levels in tap water in Gozo and agricultural activity

Abstract

Nitrate levels in drinking water have been consistently considered to be a major environmental and human health concern in many countries. Several health effects including the incidence of various cancers have been associated to high exposure of this anion. The purpose of this research is to investigate the relationship between agricultural activity and nitrate concentrations in tap water in Gozo, a small island with more than half of its surface area dedicated to agriculture. Nitrate in tap water was measured using a nitrate selective probe and secondary data such as livestock headcounts, area of arable land, nitrate in groundwater and locations of boreholes used in tap water production was gathered from the relevant government entities. These datasets were used in conjunction with the measured nitrate levels in tap water in order to determine possible relationships through both geolocation and statistical testing. The results show that there is no evident direct relationship between agriculture and nitrate in tap water due to a number of factors confound to this link. These include long percolation rates and residence times, other sources of nitrate which were not investigated by this study and the practice of pooling in of all groundwater abstracted from the boreholes into one reservoir prior to tap water production and distribution. The average concentrations of nitrate in tap water were found to be high (48.5 mg/L) and very close to the 50 mg/L limit set by the EU Nitrate Directive. An unusual pattern of different levels of nitrate in tap water was also observed. Such distinct concentrations were connected to storage reservoirs. This study answers the question regarding the correlation between agricultural activity and nitrate concentration in the tap water, but further research is needed to continue investigating such relationship.