Co-operative study of residues in drinking water: Public health laboratories - Region of Lombardy - Italy

The Department of Public Health of the Region of Lombardy, with the technic al support of the International Centre for Pesticide Safety (ICPS), has car ried out an interlaboratory cooperative studies (quality control) of pestic ide residues in drinking waters, specifically addressed to public health la boratories. Tap water fortified with known concentration of the following analytes: cer tified Atrazine, Simazine and Terbuthylazine, was used in the trial. Three distributions of samples were organized to the 13 participating laboratorie s at three months intervals (October 1997, January 1998 and March 1998). Ea ch distribution was included fourteen random specimens, i.e. two replicas o f seven different specimens, and a blank. In accordance with the current regulation, stating that concentrations of a single compound are not to exceed either 0,1 ppb or a total of 0,5 ppb (La w N.1988/236), concentrations of each analyte ranged from 0.05 to 0.50 ppb. The results obtained in the thirteen laboratories taking part in the study were collected and statistically evaluated by ICPS. In a first phase of the study laboratories were considered as a whole; succ essively as single units. Although most results were satisfactory, the calculation of z-scores showed some important differences, indicating that not all the laboratories in th e Region of Lombardy operate at the same level of quality.