title: [Monitoring of nitrate content in drinking water in Koprivnica-Krizevci County].
abstract: OBJECTIVE
  The aim of the study was to establish nitrate concentrations in drinking water originating from shallow wells across Koprivnica-Krizevci County, to assess the influence of agricultural point sources on nitrate water contamination, and to explore the correlations between water nitrate concentrations and agro-ecologic factors.
  
  
  METHODS
  During the 2002-2007 period, a total of 1170 potable water samples were taken from 104 shallow wells across Koprivnica-Krizevci County. Given the geographical and developmental determinants, the investigated area was divided into three sections: Koprivnica, Krizevci and Durdevac areas. Potable water was sampled throughout the 6-year, all season-period conformant to the HRN ISO 5667-3 standard. Nitrate concentrations in potable water samples were established using ion chromatography (HRN EN ISO 10304-1:1998). The total amount of downfalls subsequently correlated to nitrate concentrations was determined by summing up individual metric values provided by the State Meteorological and Hydrological Service. Data were analyzed in a descriptive manner and compared to the maximal allowable concentrations (MAC) stipulated under the Ordinance on Potable Water Safety, as well as to the limit values recommended under the Nitrates Directive. The X2-test produced statistically significant differences.
  
  
  RESULTS
  In 25% (n=294) of water samples, nitrate concentration exceeded MAC. The majority of unsafe samples were recovered in Krizevci area (38%; n=382), followed by Koprivnica (23%; n=613) and Durdevac area (6%; n=175). The mean range spanned from 0.1 to 279.0 mg/L, while the total mean nitrate concentration was 41.7 mg/L. The highest mean nitrate concentration of 53.9 mg/L was measured in Krizevci area, followed by 38.8 mg/L in Koprivnica and the lowest 24.9 mg/L in Durdevac area. Out of 75% of safe water samples, the measured nitrate concentration was below 25 mg/L limit value recommended under the Directive in as much as 52% of samples. Given the detected nitrate concentrations in the sampled well water, the wells were classified as satisfactory, occasionally unsatisfactory and unsatisfactory. The influence of point sources was assessed based on their distance. In roughly 50% of samples taken from occasionally or definitely unsatisfactory wells, point sources were located up to 10 meters away, while in as much as 93% of samples taken from satisfactory wells the point sources were situated over 20 meters away (p<0.01). For some of the wells, statistically significant positive (r=0.45 to 0.87) or negative (r=-0.30 to -0.66) correlations between the amount of downfalls and nitrate concentrations were established, while in the third well group this correlation (r=-0.14 to -0.24) was lacking.
  
  
  CONCLUSIONS
  The results obtained are comparable to those of similar studies undertaken in regions having a similar agro-ecological and agricultural profile. Across the Koprivnica-Krizevci County, differences in the underground water quality may arise as a consequence of water contamination due to distinctive agricultural activities. The range of the mean nitrate concentrations established in potable water samples recovered from shallow wells was wide; the total mean nitrate concentration was relatively high (41.7 mg/L). The distribution of relative concentrations revealed 25% of samples to have nitrate concentrations higher than MAC under the Ordinance. Spatial distribution revealed the majority of unsafe water samples to stem from Krizevci area (38%), consistent with the majority of large husbandries situated therein. Contaminating point sources located not farther than 10 meters from shallow wells significantly influence the quality of drawn water. Respective of correlations between the amount of downfalls and water nitrate concentrations, both negative and positive links were established.
authors.affiliation: Institute of Public Health, Koprivnica-Krizevci County, Koprivnica, Croatia.
authors.forename: Jasna
authors.initials: J
authors.lastname: Nemcić-Jurec
authors.forename: Drazenka
authors.initials: D
authors.lastname: Vadla
mesh_terms: D000383:Agriculture; D017523:Croatia; D006801:Humans; D009566:Nitrates / Q000032:analysis*; D012424:Rural Population; D014881:Water Supply / Q000032:analysis*
chemical_list: D009566:Nitrates