Determination of the taste threshold of copper in water

Copper effects on human health represent a relevant issue in modern nutriti on. One of the difficulties in assessing the early, acute effects of copper ingested via drinking water is that the taste of copper may influence the response and the capacity to taste copper in different waters is unknown. T he purpose of the study was to determine the taste threshold of copper in d ifferent types of water, using soluble and insoluble salts (copper sulfate and copper chloride). Copper-containing solutions (range 1.0-8.0 mg/l Cu) w ere prepared in tap water, distilled deionized water and uncarbonated miner al water. Sixty-one healthy volunteers (17-50 years of age), with no previo us training for sensory evaluation, participated in the study. A modified t riangle test was used to define the taste threshold value. The threshold wa s defined as the lowest copper concentration detected by 50% of the subject s assessed. To evaluate the olfactory input in the threshold value obtained , 15 of 61 subjects underwent a second set of triangle tests with the nose open and clamped, using distilled water with copper sulfate at a concentrat ion corresponding to the individual's threshold. The taste threshold in tap water was 2.6 mg/l Cu for both copper sulfate and copper chloride. The cor responding values for distilled deionized water were 2.4 and 2.5 mg/l Cu fo r copper sulfate and copper chloride, respectively. In uncarbonated mineral water the threshold values were slightly higher, 3.5 and 3.8 mg/l Cu for c opper sulfate and for copper chloride, respectively, which are significantl y higher than those observed in lap and distilled waters (P < 0.01, Kruskal -Wallis test). The taste threshold did not change significantly when the no se was clamped. In conclusion, the median values for copper taste threshold were low, ranging between 2.4 and 3.8 mg/l Cu, depending on the type of wa ter.