Phthalic acid esters in urban watercourses of Colombo and their treatment

Abstract

Urbanization of many cities with industrial, commercial, and residential areas in the world takes place at an unprecedented scale. Di-2 Ethylhexyl Phthalate (DEHP) is commonly used as a plasticizer in a number of industries which has become a precursor to cause DEHP contamination of watercourses through untreated or partially treated industrial wastewater effluents. Such contamination may result in bioaccumulation and bio-concentration in biota, so that it will adversely affect humans through the food chains. The presence of six PAEs (dimethyl phthalate (DMP), diethyl phthalate (DEP), di (n-butyl) phthalate (DBP), benzyl butyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di(n-octyl) phthalate (DnOP)) in 22 shallow urban watercourses in Colombo and suburbs of Sri Lanka was investigated and the effect on fish community was analyzed. EPA 8061A method was used in analyzing PAE concentrations in samples and Gas Chromatography / Mass Spectrometer was used. Titanium dioxide (TiCb) and Modified Coal-derived Fly Ash (MCFA) were successfully synthesized and characterized using Fourier-Transform Infrared Spectroscopy, Environmental Scanning Electron Microscopy, and X-ray diffraction. Effectiveness and efficiency of TiC>2 and MCFA in the removal of DEHP from wastewaters was identified. According to the results obtained, the average concentrations of DEP, DBP, BBP, and DEHP in all watercourses varied between 2.5-265.0, 1.0-32.0, 61-108, and 12— 165 pg/L, respectively. DMP and DnOP values were below the limits of quantification (DMP-0.5 pg/L, DnOP-l.O pg/L) for all watercourses. DEHP was the most abundant PAE in many watercourses. The significant factors affecting the ubiquitous presence of PAEs in watercourses are the inherent properties of each PAEs, the presence of industrial and household products with great potential for the migration of PAEs in the sub-catchments, and the quality of receiving water. The contamination levels of PAEs in most of the watercourses are alarmingly high, as evidenced by higher concentrations of DEHP and DBP than those of Canadian permissible levels for the protection of aquatic life (16 and 19 pg/L). iii Isolated lakes which are not adjoining to urban industries, showed depleted adverse effects, most of the urban lakes were observed a significant potential for adverse effects on fish. Thus, the ecological risk of PAEs in urban watercourses in Sri Lankan environments should be considered. TiC>2 nanoparticles were used to remove DEHP through photocatalysis. The photocatalysis with TiC>2 for the destruction of DEHP was found to be a promising technique in removing DEHP from industrial wastewaters. The most economical dosage of TiC>2 would be one gram and it needs to be photocatalysed for a period greater than 44 minutes for complying with the permissible level stipulated for DEHP (16 pg/L) for the protection of aquatic life. The cost of the photocatalysis with Ti02 was around Rs.120 and the cost could be further reduced when the material (TiC>2) is reused for subsequent usage. Even TiC>2 was reused for five times, inherent properties for photocatalysis were not changed. An initial level of 171 pg/L of DEHP was successfully removed with 98% efficiency by three grams of MCFA dosage and consequently, regenerated with NaOH twice for the effective use. The maximum monolayer adsorption capacity of MCFA was 63.6 pg/g of DEHP. MCFA is a potential candidate for the effective removal of DEHP from industrial wastewaters as its raw materials are readily available.