Determination of organically bound chlorine in industrial and environmental samples

Abstract

Several alternative methods for determination of organically bound chlorine (OCl) in pulp mill effluents and sludges, surface waters and sediments were evaluated. Methods for partial OCl parameters, such as extractable organic chlorine (EOCl) and extractable persistent organic chlorine (EPOCl) were also studied. Measurements of inorganic chloride (Clˉ) and total chlorine (TCl) were undertaken to cross-check the results. Effluent and water samples were analysed using a method based on the enrichment of OCl onto XAD-2/8 resins followed by oxygen combustion and chloride ion determination either by an ion-selective electrode or ion chromatographic detection. XAD-2/8 resins were also used to desalt samples of brackish waters. OCl in sediment and sludge was converted to chloride ions either by wet combustion with sulphuric acid or by oxygen combustion after removing the inorganic chloride originally present in the analysed samples. Chloride concentration was determined by conventional potentiometric titration, by a chloride-selective electrode or by an ion chromatographic method. Oxygen combustion was used in the analysis of TCl in the original samples, EOCl in solvent extracts, and EPOCl in sulphuric-acid-treated solvent extracts. The precision and recovery of the methods were generally good, and none of the proposed methods requires expensive instruments. In a series of case studies, OCl and related parameters were determined for samples taken from pulp mills and their recipient environments in the Äänekoski-Päijänne watercourse in Central Finland, the river Kymijoki in Southeast Finland, the Pietarsaari Archipelago and Lake Baikal. The OCl, Clˉ and OM sum parameters showed a clear decreasing gradient from the vicinity of the pulp mill to more remote places. Close to the point of discharge concentrations of OCl were about 200 μg Lֿ¹ in water and up to 14 mg gֿ¹ in sediment. In dated sediment cores from pulp mill recipients a very significant increase of OCl and OM towards younger layers demonstrated the history of pulp bleaching. The EOCl/OCl ratio in surface sediment decreased with increasing distance from the pulp mill.