Inorganic Nitrogen Compounds in Water Mains in Northern Poland and Their Implication for Health Risk

摘要

The presence of nitrogen compounds significantly affects the quality of water intended for human consumption. The maximum contaminant level (MCL) of nitrogen in potable water in Poland was set up as follows: NO_2~--0.5 and NO_3~--50 mg=L, NH_4~+-0.50 mg=L. For this reason, the objective of the study was to monitor the chemical composition of water as a priority basis for the water quality information system to provide consumers with water that meets the appropriate health and quality standards. The results of a multiyear study (1992-2003) carried out in four regions and at 12 monitoring sites in northern Poland showed NO_2~-and NO_3~-levels significantly below MCL limits. Low nitrate concentrations in water drawn from Quaternary water-bearing horizons indicate the absence of point sources of pollution. Ammonia levels exceeded MCL values at every monitoring site. Supernormal ammonia concentrations in raw water are indicative of the natural origin of ammonia ions. They are correlated with the depth of the water-bearing horizon, and they occur when nitrate and nitrite levels are low. Following water treatment, the drop in nitrogen levels differed at every monitoring point. The highest reduction was noted in the ?u?awy Water Mains (?WM) where the average NH_4~+ concentrations decreased from 2.30 mg=L in raw water to 0.34 mg=L in treated water. In general, the highest drop in ammonia ion levels was reported in water samples which were marked by the highest initial ammonia concentrations. A secondary increase in ammonia concentrations was observed during the process of water distribution to consumers, subject to the type and age of the distribution network. The results of this study indicate that water quality has to be closely monitored for the needs of public health protection.