Formation of genotoxic compounds by medium pressure ultraviolet treatment of nitrate-rich water

Abstract

A B S T R A C TGenotoxic compounds were produced by full-scale medium pressure (MP) ultraviolet hydrogen peroxide (UV/H 2 O 2 ) treatment of nitrate-rich pretreated surface water. It was hypothesized that this formation was caused by the reaction of nitrate photolysis intermediates with natural organic matter (NOM). An increase in the Ames test response was also found after MP UV photolysis of water containing Pony Lake NOM from the International Humic Substances Society (IHSS) and nitrate, while no increase in the Ames test response was found when nitrate was absent. The same trend in an Ames test response and nitrite formation was observed for both nitrate-rich pretreated surface water and reconstituted water containing NOM and nitrate. Therefore, the conversion of nitrate by MP UV photolysis was studied in several water types. In organic-free water, nitrate was completely converted into nitrite, while no inorganic nitrogen was lost. Also in nitrate-rich surface water, nitrite was found as the only inorganic reaction product, while a small decrease of the inorganic nitrogen content was observed. When NOM was replaced by phenol, MP UV photolysis caused a restricted nitrite formation only, together with a large loss of inorganic nitrogen. The formation of the nitrated phenol derivatives, 2-and 4-nitrophenol and 4-nitrocatechol, was observed with highest concentrations under practical UV conditions. It is hypothesized that the formation of nitrated aromatic compounds is the cause of the increased Ames test response by MP UV treatment.

Influence of process conditions and water quality on the formation of mutagenic byproducts in UV/H2O2 processes

“…Guzella et al (2002) reported that O 3 /UV and O 3 /H 2 O 2 /UV processes may increase the mutagenicity of treated water, although it was noticed that adsorption to granular activated carbon (GAC) may effectively remove the toxic byproducts. This is in accordance with other research (Heringa et al, 2011;Penders et al, 2012;Hughes et al, 2013;Martijn et al, 2014), which showed that treatment with UV/H 2 O 2 may result in the formation of compounds which cause a positive response in the Ames fluctuation assay. GAC, applied to remove the excess of H 2 O 2 , was shown to effectively eliminate the mutagenic activity of drinking water treated with UV AOP.…”

Tracing Nitrogenous Disinfection Byproducts after Medium Pressure UV Water Treatment by Stable Isotope Labeling and High Resolution Mass Spectrometry

“…Samples were treated with MP UV using a collimated beam (CB) setup. Concentrations of NOM and nitrate and experimental MP UV conditions were chosen at a level that positive responses in the Ames fluctuation test were expected, based on previous experiments, and thus potentially mutagenic compounds are presumably formed. Control samples were also prepared, i.e.…”

“…Genotoxicity of treated drinking water is regularly evaluated by the Ames mutagenicity test. Effluents of MP UV/H 2 O 2 drinking water treatment have been shown to induce a response in the Ames fluctuation test, indicating the presence of potentially mutagenic compounds. − The genotoxic effect was shown to be effectively removed by post-treatment with granular activated carbon (GAC) filtration, which is applied to remove the excess of H 2 O 2 . , Nitrate photolysis by MP UV irradiation in the presence of natural organic matter (NOM) was found to be the key parameter in the manifestation of an Ames test response after treatment of pretreated surface water, reconstituted water, and artificial water containing NOM and nitrate with MP UV technology. , The formation of nitro- or nitroso aromatic compounds due to nitrate photolysis by MP UV irradiation in the presence of NOM is likely. Some nitro- and nitroso aromatic compounds are known to produce a response in the Ames test. ,− The Ames test response observed after MP UV irradiation may be caused by multiple nitrated and nitrosated compounds at different concentrations.…”

“…In order to quantify the total mutagenic effect of MP UV irradiation of water containing nitrate and NOM, preceding studies converted the Ames test response into 4-nitroquinoline oxide (4-NQO) equivalents, a known genotoxic compound commonly used as positive control in the Ames test. This showed that MP UV treatment of artificial water resulted in the formation of 120 ng/L 4-NQO equivalents in the water extracts. , Since a Threshold of Toxicological Concern (TTC) of 10 ng/L has been derived for genotoxic substances in drinking water, only concentrations below this level are generally considered to pose a negligible human health risk. The relevance of these DBPs for public health should thus be further investigated.…”

Induced Genotoxicity in Nitrate‐Rich Water Treated With Medium‐Pressure Ultraviolet Processes

“…In our experiments, this gap was not observed, while in a first broad screening research effort, no nitroaromatics were found after MP UV treatment of CSF‐pretreated IJssel Lake water. However, when the organic water matrix was replaced by phenol, a large gap in the nitrogen balance was observed and formation of a number of nitrophenols was found (Martijn et al 2014). In a second broad‐screening research effort with synthetic water containing IHSS Pony Lake NOM and N 15 nitrate, the formation of over 100 nitrated organic compounds in low concentrations was observed (Vughs 2014).…”