NITROGEN TRICHLORIDE (NCl3) DETERMINATION IN INDOOR SWIMMING POOLS: PROPOSAL FOR A NEW METHOD.

It is well known that water disinfection treatments in indoor swimming pools generate a mixture of potentially harmful disinfection by-products (DBPs). Among them, nitrogen trichloride (NCl3), a powerful irritant, has been linked with respiratory symptoms and asthma in swimmers, mainly in children, and in occupationally exposed subjects. Accurate NCl3 exposure assessment in indoor swimming pools is difficult, because NCl3 presence in air is influenced by different factors, including the pool water quality and the number of swimmers in the pool. Moreover, the analytical method usually adopted for the determination of NCl3 in air samples shows some problems such as the use of particular filters for the air sampling procedures and the expansive instrumental equipments for the laboratory quantification of this volatile DBPs. The aim of this study was to identify a new analytical method for NCl3 air determination that could be used directly in swimming pool facilities for the human exposure assessment procedures. This new protocol is based on a colorimetric reaction commonly employed to detect the total and free chlorine levels in water. Particularly, it allows the entrapment of NCl3 in air into a water solution containing diethyl-p-phenylenediamine (DPD 1) and Potassium Iodide (DPD 3). Therefore, NCl3 from the air environment reacts with DPD 3 realising iodine, which reacts with DPD 1 and produces a pink colour. The intensity of the colour is proportional to the amount of NCl3 from the sampled indoor swimming pool air, and can be easily measured using a portable photometer for DPD analyses.The proposed method has been validated in terms of linearity, limit of detection (LOD) and repeatability. We tested the linearity by creating an artificial swimming pool environments under a closed chemical safety cabinet, and reading solutions of NCl3 in air sampling deriving from standards in water at different concentrations (5, 10, 20 mg/l of NCl3 standards). The actual concentration of NCl3 in the water was verified by adopting the same DPD method used in the real swimming pools. This linearity test was repeated three times and showed R2 values of: 0.996; 0.998 and 0.996. The LOD was measured either as standard deviation, which according to the instrument sensitivity and liters of air sampled, has values of 3.6 and 8.5 mg/l respectively. The repeatability showed a coefficient of variation (CV%) equal to 1.7%. The proposed method which is patent pending, is a method that does not use toxic substances, is easy to use, efficient and economical and gives good results in terms of linearity and repeatability.