Toxic metals, nitrates and nitrites in water and residues in bovine milk

Water with toxic metals represent a risk to animal production and to public health due to their presence in milk. The information of the chemical quality in water for animal consumption in the milk basin of Xochimilco, Mexico is scarce. A water sampling was carried out to identify arsenic, lead, mercury, nitrates and nitrites, pH, temperature, colour and smell in four dairy farms in winter season, 2017. The toxic metals were identified by qualitative Reinsch test and the concentration by flame atomic absorption spectrometry technique. The results of pH and temperature showed an average of 7.8, and of 10.5 ºC, the mean nitrate content was 0.79 mg L-1and 0.070 mg L-1for nitrites. Reinsch test indicated that all water samples were positive for at least one metal, with mercury being the most frequent (66%). The detected mean concentrations were: lead (0.040±0.03 mg L-1), arsenic (0.0015±0.0011 mg L-1), cupper (0.019±0.0053 mg L-1), cadmium (0.039±0 mg L-1), all inside the livestock maximum permissible levels, while mercury (0.078±0.03 mg L-1) was found in excess. Arsenic was the only metal found inside the drinking water permissible levels and cupper was found in the limit of the drinking water. In milk samples, lead and cadmium were found. It is concluded that the contamination by toxic metals in the water of dairy cows consumption in the Xochimilco Basin, can affect milk production, and lead canbe a risk in human healthin a long term exposure.