Potential of analytical laboratories of lead and cadmium in water in Thailand during 2008 - 2014

Abstract

       Bureau of Quality and Safety of Food (BQSF), Department of Medical Sciences, conducted a proficiency testing (PT) program on analysis of heavy metals; Pb and Cd in water in order to evaluate the competence of participating laboratories during 2008-2014, (7 rounds). Homogeneous PT sample of water for analyzing lead (Pb) and cadmium (Cd) were delivered to the laboratories that would send the results back within a designated time. The results were analyzed statistically using the z-score to assess the ability of participating laboratories. More than thirty laboratories participated in the PT programs each year. There were 12 and 8 laboratories that enrolled the Pb and Cd schemes, respectively for all 7 rounds. It was revealed that there were six Pb laboratories and five Cd laboratories having satisfactory results in every round, with the percentage of 50.0 and 62.5, respectively. Trends of participating laboratories quality which their continual PT results showed by z-score calculated from s value can be determined. The laboratories could perform continuous self-evaluation by calculating percentage of pooled relative standard deviation (%rsd_pooled) of previous round which was subsequently used to compute pooled standard deviation (s_pooled), resulting the z-score. For Pb scheme, it was found that new z-scores of a laboratory were lower than the assigned values in all rounds. Although obtaining the satisfactory z-scores, such laboratory should find out the causes and correct those problems. For Cd scheme, all laboratories could maintain quality of their performance at satisfactory level. In conclusion, the evaluation of successive PT results could indicate potentiality of laboratories by considering trends in either direction of the results. This would enable water analysis laboratories in Thailand to improve and develop their competence and to achieve the same standard.