A HPLC method for the simultaneous determination of three widely used antihistaminic drugs, diphenhydramine, oxatomide and promethazine, in surface water samples and a toxicological assay using the bioluminescent bacterium Vibrio fischeri to assess a comprehensive contamination were developed. The analytical procedure was extended to the by-products from promethazine photodegradation. The method involved pre-concentration and clean-up by solid phase extraction and HPLC analysis with diode array detection. Validation of the method was performed on synthetic mixtures and surface water samples spiked with the drugs, showing mean recovery ranging from 93 and 107%, with RSD below 5.5%. Limits of quantitation in surface waters, calculated on 1.0 l of sample, were in the range 1.9 – 2.5 μg/l.
The toxicological tests demonstrated toxicity due to promethazine from a concentration of 3.94 μg/ml while the other antihistamines showed no significant toxicity up to 50.0 μg/ml. However, the toxicity of drug mixtures was found greater than the sum of the values from samples containing single drugs. The presence of the studied drugs was monitored in waters sampled from two rivers in Calabria (Italy), collected along a period of seven months. Diphenhydramine and oxatomide were not detected in any samples. On the contrary, promethazine was found in two samples taken in July at a concentration of 2.0 and 2.3 μg/l, significantly below the values causing toxicity.