Perfluorinated compounds and trihalomethanes in drinking water sources of the Western Cape, South Africa

Abstract

This study focused on quantifying two types of internationally regulated contaminants found in drinking water: 1) Trihalomethanes (THMs) and 2) Perfluorinated compounds (PFCs). The first contaminants monitored were THMs, classified as a group of chemicals that are formed along with others during the disinfection of water using liquid chlorine, chlorine dioxide or chlorine gas. Hence, the resulting compounds are called disinfection by-products (DBPs). The disinfectant reacts with natural organic matter in water to form common THMs, which include chloroform (CHCl3 or CF), bromodichloromethane (CHCl2Br or BDCM), dibromochloromethane (CHClBr2 or DBCM) and bromoform (CHBr3 or BF), with chloroform being the most common in chlorinated water systems. The current study has focused on THMs for two primary reasons: 1) THMs have raised significant concern as a result of evidence that associate their presence in drinking water with potential adverse human health effects, including cancer and 2) the levels of THMs in drinking water post-treatment is not monitored regularly in South Africa and thus far, there is inadequate and limited information about their concentration levels for drinking water treatment plants (DWTPs) and distribution stations (DWDSs) of the Western Cape, South Africa before, distribution to various suburbs, including townships. THMs normally occur at higher levels than any other known DBPs and their presence in treated water is a representative of the occurrence of many other DBPs. THMs were quantified in chlorinated drinking water obtained from seven (7) DWTPs, namely; Atlantis, Blackheath, Faure, Brooklands, Steenbras, Voelvlei and Wemmershoek, and one DWDS in Plattekloof. This included determining THMs concentration in tap water collected from various suburbs including townships, to assist local authorities in obtaining information on their concentration and whether or not the presence of residual chlorine and organic matter on post-treatment results has increased THMs at the point of use. THM analysis was performed using liquid-liquid extraction/gas chromatography with electron capture detector (LLE-GC-ECD) analytical process according to the EPA method 501.2, which was used with minor modifications. The instrument operational conditions were as follows: Column → DB5-26, 30 mm, 0.53 mm, 1.0 μm df HP-1 (Agilent Technologies, USA); Carrier gas → Helium at a constant inlet pressure of 15 kPa; Make-up gas → 99.9% Nitrogen gas at 60 L/min; Injector temperature → 40°C; Oven temperature → 270°C and Detector temperature → 300°C. Since natural organic matter (NOM) in raw water is a precursor for THM formation, NOM analysis was performed as total organic carbon (TOC) using Spectroquant TOC test kits. Other drinking water quality parameters analysed were pH, residual free chlorine, conductivity and total dissolved solids (TDS). The average Total THM concentrations detected from seven of the DWTPs, including the DWDS, ranged from 26.52 μg/L (for Plattekloof) to 32.82 μg/L (for Brooklands), with the observed concentrations being comparable. The average chloroform concentrations were the

highest in all the water samples, ranging from 11.74 μg/L (for Plattekloof) to 22.29 μg/L (for Voelvlei), while DBCM had the lowest concentration. The only DWTP that was not comparable with the seven DWTPs was Atlantis, with the highest average TTHM concentration of 83.48 μg/L and a chloroform concentration of 46.06 μg/L. From the tap water samples collected from 14 Western Cape suburbs, the average TTHM concentrations ranged from 5.30 ug/L (for Mandalay) to 13.12 μg/L (for Browns Farm, Philippi), and all these concentrations were lower than the TTHM concentrations detected in the water samples from the DWTP. Overall, the average total THM and individual THM species concentrations were below the recommended SANS 241:2011 and WHO drinking water guideline limits. This included the observed pH (6.39 to 7.73), residual free chlorine (0.22 to 1.06 mg/L), conductivity (121 to 444 μS/cm), TDS (93.93 to 344.35 mg/L) and TOC (0.38 to 1.20 mg/L). All these water quality parameters were within the specification limits stipulated in SANS 241. However, the average residual free chlorine concentration for Atlantis was very low (0.06 mg/L), which was below the WHO minimum residual free chlorine concentration guideline value of 0.2 mg/L for a distribution network – an indication that suggested the need for a re-chlorination station prior to distribution to households. Low chlorine content might result in the formation of unwanted biofilms in the distribution network, thus reducing the organoleptic properties of the water. Additionally, there was no direct link between several water quality parameters quantified (i.e. pH, TOC and water temperature) to TTHM formation. However, a high chlorine dose was observed to result directly in a higher concentration of chloroform in treated water prior to distribution. The second contaminants monitored were Perfluorinated compounds (PFCs), which are non-biodegradable, persistent and toxic organic chemicals known for their ability to contaminate environmental matrices, including drinking water sources. In recent years, many researchers considered it essential to identify and quantify PFC levels in drinking water worldwide with the main focus being on the two most abundant PFCs; namely Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS). Their toxic effects to human health, plants and wildlife were also evaluated, classifying them as possible carcinogens. We know from the literature reviewed that, although the presence of PFCs in drinking water has been documented worldwide, there is limited information about their presence specifically in South African drinking water sources, even about less studied PFCs such as Perfluoroheptanoic acid (PFHpA), Perfluorododecanoic acid (PFDoA), Perfluorononanoic acid (PFNA), Perfluoroundecanoic acid (PFUA), Perfluorodecanoic acid (PFDeA) and the well-known PFOA including PFOS. Although several other PFCs have been detected in water sources and reported in various studies, the USEPA only issued drinking water guideline limits for Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS) of 400 ng/L and 200 ng/L, respectively, with no mention of the other PFCs. However, these PFCs have similar properties to those of PFOA and PFOS as they have been shown to impose similar detrimental health effects on human health. This study thus

focused on the detection of PFCs in both raw and treated drinking water in the Western Cape DWTPs such as Atlantis, Blackheath, Faure, Brooklands, Steenbras, Voelvlei and Wemmershoek, and one DWDS in Plattekloof. Water samples (raw and treated water) used in this study for PFC analysis were collected in 2L polypropylene screw capped bottles. PFC analysis was performed in four sample batches for each location collected through the period of October to December 2012 (summer). PFCs were analysed in accordance with a modified EPA method 537, which entails solid phase extraction (SPE) followed by analysis using a liquid chromatography/tandem mass spectrometer (LC/MS/MS). The slight modification was with the water sample volume used for extraction, which was increased from 250 mL to 500 mL. The instrument used was an HPLC - Ultimate 3000 Dionex HPLC system and MS model - Amazon SL Ion Trap, with the following MS/MS operational conditions and Ion mode: MS Interface → ESI; Dry temp → 350C; Nebulizing pressure → 60 psi; Dry gas flow → 10 L/min; Ionisation mode → negative; capillary voltage → +4500V; End plate offset → −500V while the separation column was a Waters Sunfire C18, 5 μm, 4.6 × 150 mm column (Supplier: Waters, Dublin, Ireland) with an operational temperature of 30C. From the results obtained in this study, seven different PFCs (i.e. PFHpA, PFDoA, PFNA, PFUA, PFDeA, PFOA and PFOS), were detected in raw and treated water with PFOA and PFOS being the least detected PFCs as they were detected only in raw water (PFOA) from Faure, as well as raw and treated water (PFOS) from Brooklands. The highest concentration observed in treated water was for PFHpA, which was quantified at a maximum average concentration of 43.80 ng/L (Plattekloof). The maximum average concentrations of other PFCs detected were as follows: PFDoA - 4.415 ng/L for Faure raw water; PFNA - 2.922 ng/L for Plattekloof outlet; PFUA - 7.965 ng/L for Brooklands treated water and PFDeA - 2.744 ng/L for Faure raw water. Another observation from the results was that the concentration of the majority of the PFCs detected in treated water was higher than that quantified in raw water, suggesting possible contamination by materials used during water treatment. In conclusion, THMs detected in treated water from various DWTPs and one DWDS in the Western Cape met the required local and international drinking water quality guidelines, while the presence of PFOS, PFOA, PFHpA, PFDoA, PFNA, PFUA and PFDeA in treated water requires that local water professionals continue to monitor their presence to ensure that measures for their reduction are in place. Furthermore, the National standards (SANS 241) for municipal drinking water guidelines must be updated to include the monitoring of PFCs, including the lesser known and less studied PFCs such as PFHpA, PFDoA, PFNA, PFUA and PFDeA.