Peter Backlund

Degradation products formed during UV-irradiation of humic waters

Natural humic lake water and aqueous solutions of humic substances were treated with ultraviolet (UV) radiation (λ = 254 nm). The effects on the dissolved organic carbon content (DOC) and the absorbance at 254 nm (Abs254) and 460 nm (Abs460) were monitored and the identity and concentrations of gas chromatographable organic degradation products were determined. The DOC content and the (Abs254) of the humic solutions decreased continuously with increasing UV-dose. Several aromatic and aliphatic degradation products were identified and roughly quantified The concentrations of aromatic hydroxy carboxylic acids and hydroxy aldehydes increased when relatively low UV-doses were used, but declined following further irradiation. The concentrations of aliphatic dibasic acids increased over the full range of UV-doses

DEGRADATION OF AQUATIC HUMIC MATERIAL BY ULTRAVIOLET LIGHT

Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide . The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined. The DOC content and the UV-abs. of the water decreased substantially during treatment with. The decreases were dependent on the time of irradiation (UV dose) as well as on the H2O2 dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and waters, respectively. No mutagenic activity was generated by the UV irradiation or the treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step.

Impact of UV254-radiation on aquatic humic substances

Aqueous solutions of humic substances (humic and fulvic acids) were exposed to UV-radiation at 254 nm (UV254). The induced changes in the dissolved organic carbon content (DOC), in the absorbance of radiation at 272 nm (A272), and in the solid state 13C NMR spectral data were recorded. During the first 40-h exposure of the humic acid solution, the DOC-normalised UV272-absorbance (A272/DOC ratio) was approximately constant, indicating a fairly high mineralisation rate as compared to the rate of the degradation of UV272-absorbing structural subunits. During prolonged exposure, however, the mineralisation rate was clearly retarded. The corresponding normalised values for the fulvic acid solution demonstrated that the relative “rate of mineralisation” was constantly lower. Fulvic acid was more susceptibile for UV-initiated degradation than humic acid. The NMR spectra revealed that the high-molecular-weight matter in both of the exposed samples changed to a more aliphatic character and that more carboxyl and carbonyl carbon atoms appeared.

Mutagenic activity and presence of the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2-(5H)-furanone (MX) in chlorinated raw and drinking waters in the Netherlands

Chlorinated surface and drinking waters in The Netherlands were analysed for mutagenic activity (Ames test) and the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Mutagenic activity and MX were formed during chlorine treatment of raw surface waters and purified surface water. Mutagenicity was also present in finished drinking waters which had been subjected to post-chlorination, but no MX could be detected. It is proposed that the mutagens responsible for most of the activity are acidic compounds as they were mainly extractable under acidic conditions. The precursors to the mutagenic compounds formed during post-chlorination of drinking water were efficiently removed by use of ozonation/activated carbon filtration. On the other hand, coagulation (Fe(III] in the presence of activated carbon powder seemed to have hardly any effect on the mutagen precursors. The calculated mutagenicity contribution from MX to the observed TA100 activity in the waters studied was less than 20%.

Formation of AMES mutagenicity and of the strong bacterial mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone and other halogenated compounds during disinfection of humic water

Humic water was treated with different disinfectants and examined for mutagenicity, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), E-2-chloro-3-(dichloromethyl)-4-oxobutenoic acid (E-MX), adsorbable halogenated organics (AOX), and chloroform. The highest mutagenic activity and the highest concentrations of MX and E-MX were noted for water disinfected with chlorine. An increased proportion of chlorine dioxide in the combined chlorine/chlorine dioxide treatment resulted in a decrease in the mutagenic activity and in the concentrations of MX, E-MX, AOX and chloroform. Ozone treatment prior to chlorination gave a slight decrease in mutagenicity and in the concentrations of MX and E-MX. Although the amount of AOX in monochloramine treated water was comparable to that in chlorinated water chloramination produced considerably lower mutagenicity and lower concentrations of MX and E-MX. MX was responsible for 20 – 50% and E-MX for a few percent of the mutagenic activity generated by the disinfectants.

Bacterial growth in humic waters exposed to UV-radiation and simulated sunlight

Sterile filtered (0.45 μm) humic lake water was exposed to simulated sunlight (300–800 nm) or UV-radiation (254 nm) for various periods of times and the dissolved organic carbon content, absorbance at 254 and 460 nm and pH were recorded. The irradiated water was inoculated with a natural bacterial assemblage and the number of viable bacteria was estimated 3 and 5 days after the inoculation using the plate count technique. The number of viable bacteria increased with the irradiation time indicating that the chemical changes of the humus macromolecules observed during irradiation resulted in an increased availability of the dissolved organic material as bacterial substrate. No inhibitory effect on the bacterial growth, due to the presence of toxic organic reaction products, was observed.

Mutagenic activity in humic water and alum flocculated humic water treated with alternative disinfectants

Mutagenic activity in Salmonella typhimurium strains TA 100, TA 98 and TA 97 has been determined for humic water and alum flocculated humic water, treated with the alternative disinfectants chlorine, ozone, chlorine dioxide, ozone/chlorine and chlorine/chlorine dioxide. The most pronounced activity was found for chlorine treated water tested on strain TA 100 without metabolic activation (S9 mix). Ozone treatment prior to chlorination did not alter the activity, while treatment with chlorine in combination with chlorine dioxide reduced the activity to a level somewhat over the background. No mutagenic response was detected in waters treated with ozone or chlorine dioxide alone. In presence of S9 mix all water extracts studied were non-mutagenic.

Elaidic and trans-vaccenic acids in plasma phospholipids as indicators of dietary intake of 18:1 trans-fatty acids

Octadecenoic (18:1) trans-fatty acid fractions from margarine, butter and plasma phospholipids (PL) were isolated by silver ion TLC, and nine positional isomers (n-11-n-3) were identified by GC-MS based on their ozonolysis products. The GC analysis of the isolated fractions gave similar peak profiles and separated seven trans-isomers (n-11-n-6 and n-3). Without a preceding isolation step, the reproducibility of the GC method for plasma PL elaidic (18:1 n 9 trans) and trans-vaccenic acids (n-7) was 3.4 and 2.7% (R.S.D.), respectively. These trans-isomers were rapidly incorporated and cleared in plasma PL and they closely reflected both increased and decreased intake of 18:1 trans-fatty acids during moderate fat substitutions. Significant associations between high-density lipoprotein cholesterol (HDL-C) and PL elaidic and trans-vaccenic acids appeared in habitual margarine users only.

Light-induced degradation of DDT in humic water

Abstract Humic water, spiked with DDT (13 nM), was subjected to ultraviolet radiation with a wavelength of 254 nm (UV254) and also to intense simulated sunlight. Sample extracts were analysed by gas chromatography/mass spectrometry ( GC MS ), the mass spectrometer working in the selective ion monitoring mode. DDT was degraded both by the UV254-radiation and the amplified artificial solar radiation. The degradation rate was substantially faster during UV-irradiations (minutes) than during the simulated sunlight-irradiations (hours). The presence of natural dissolved organic matter had a retarding effect on the photolytic degradation rate of DDT in the UV254-experiment, but an accelerating effect in the artificial sunlight-experiment, indicating that different reaction pathways are involved in the two experiments. The formation of associates between DDT and dissolved organic matter seems to promote the photolysis induced by the UV-radiation.

Influence of chlorination pH and chlorine dose on the formation of mutagenic activity and the strong bacterial mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-5(2H)-furanone (MX) in water

Abstract Samples from two Dutch raw water sources were chlorinated in the laboratory at different pH:s and chlorine doses, and were analysed for mutagenic activity and the mutagenic compound 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Chlorination produced mutagenic activity as well as MX in both waters. The formation of MX was favoured by acidic reaction conditions and high chlorine doses, but in waters treated with excess chlorine at pH 9, no MX was detected. The mutagenicity was approximately on the same level after chlorination of both water types but the MX concentration was significantly higher in the water containing mainly humic material. MX was found to be quantitatively extracted from acidified waters by the XAD resin adsorption technique.