Determination of organically combined chlorine in high molecular weight aquatic organics

Abstract

A procedure for measuring organically combined chlorine (TOC1) in water or wastewaters is described. TOCl is measured after preconcentrating the sample, photolyzing the organics to mineralize the chlorine, and measuring inorganic chloride. The results show that chlorination of wastewater treatment plant effluents leads to significant accumulation of organically combined chlorine. From 0.0025 to 0.007 mol of TOCl per mol of TOC is produced.Production of low molecular weight organic compounds containing covalently bound chlorine during chlorination of water and wastewater is well documented (1 1. The presence of these compounds is of concern because some are carcinogenic to mammals and toxic to aquatic biota. Haloforms and chlorophenols are representative of the types of compounds generally detected. Unfortunately, analytical techniques suitable for low rnolecular weight and volatile compounds (gas chromatography, GC-mass spectroscopy, liquid chromatography) are not applicable to large, nonvolatile compounds. High molecular weight compounds such as lignins, humic acids, and polymeric nucleic acids are present in natural waters and have reactive sites for chlorine addition. The ultimate fate of such organochlorine compounds is not known, but degradation could lead to formation of low molecular weight organochlorine compounds. Development of a photochemical oxidation technique to measure the total organic chlorine (TOCI) of aqueous organics was the purpose of this study. Measurement of TOCl is preferred because specific compound identification of naturally occurring mixtures of high molecular weight organics is not feasible.A method for (determination of TOCl, by adsorbing organics on activated charcoal, washing to remove free C1-ions present, followed by pyrohydrolyzing to liberate organic chlorine as HCl, and determining C1 microcoulometrically, has been described ( 2 ) ; the method has several disadvantages. Activated carbon adsorption is not as effective for polar organics as for nonpolar organiics. Fractionation of high molecular weight material to characterize TOCl as a function of the size oforganics cannot be conveniently done. A large quantity of activated carbon must be combusted with the organic matter of interest. Chlorinated and brominated nonpolar hydrocarbons in water have been measured by neutron activation analysis (3). This method is very sensitive but requires complete elimination of inorganic halide by extracting the organics with a nonpolar solvent. An elegant method for measuring the concentration of chlorinated and brominated organic compounds using an element-specific microwave plasma detector coupled with a GC separation has been reported ( 4 ) . This method is limited by the GC pre-separation method to volatile compounds. The photochemical method offers the advantages of measuring all chlorinated organics or TOCl determination of molecular size fractionated organics; the oxidation technique can be used with any preconcentration technique. 'FOCI measurements 5,hould be useful for evaluation o...

Adsorption of dissolved organics in lake water by aluminum oxide. Effect of molecular weight

“…Several authors have noted that this public and scientific concern should be extended to include all organochlorine compounds formed, especially since the total organic chlorine produced is much greater than the chlorine present in THMs (14,15,19,53). Two studies have reported that high molecular weight organochlorine compounds are formed during the chlorination of surface waters (14,27), and the health risks of these compounds are unknown.…”

“…For water-treatment practice, we need to determine whether molecular weight fractionation occurs during adsorption by aluminum oxide. Such a fractionation could be significant in the light of recent reports that chloroform and other organochlorine compounds are preferentially produced by particular molecular-weight fractions (25)(26)(27).…”

Adsorption properties of soil humic and fulvic acids by hematite

“…Many researchers have suggested preferential adsorption of some molecular size fractions, for examples, high molecular weight (McCahill et al, 1980;Ochs et al, 1994), intermediate molecular weight (Wang et al, 1997) and hydrophobic fractions (Davis and Gloor, 1981;Gu et al, 1994). Because the adsorption of the HMW onto minerals is kinetically slow and unstable, it is difficult to properly analyze the adsorption of humic substances (Wang et al, 1997).…”