Last Month's Most Accessed Feature: Smokey water: Tobacco nitrosamines are disinfection byproducts
- Published: Mar 10, 2014
- Categories: Base Peak
Water treatment plants are there to prevent harmful compounds reaching the wider environment or entering our drinking water and by-and-large they perform that duty remarkably well. But not always. Ironically, the treatment process itself produces a number of unwanted products that have been labelled disinfection byproducts (DBPs), some of which are potentially carcinogenic. These are the group known as nitrosamines, several of which have been identified and measured in the effluent from wastewater plants. The most common of these is N-nitrosodimethylamine (NDMA).
Although several nitrosamines are known to be present in water, there are a lot more yet to be discovered according to a published N-nitrosamines assay. It revealed a total load far in excess of those that are already accounted for. This discrepancy led a group of scientists in North America to look for sources of other nitrosamines and they focused on those related to tobacco.
Xing-Fang Li and colleagues from the University of Alberta, Edmonton, Canada and the Metropolitan Water District of Southern California, La Verne, USA thought that the so-called tobacco-specific nitrosamines (TSNAs) might be found in water. They are present in tobacco smoke and are known to be carcinogenic. They could emerge in smokers’ urine to contaminate water supplies, or might also be found in water following their formation during the disinfection process.
Their suspicions could not be realised straightaway because they needed a sensitive method for detecting and measuring TSNAs in water down to their expected ng/L levels. They decided to use LC/MS because of its earlier success on other nitrosamines in water.
Aqueous solutions of five TSNAs were made up to help with method development. They were N-nitrosonornicotine (NNN), N-nitrosoanabasine (NNB), N-nitrosoanatabine (NAT), 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK) and 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanol (NNL), which are known from their association with tobacco smoke.
Each solution was injected onto a C18 HPLC column that was linked to a mass spectrometer operating in positive-ion mode under multiple reaction monitoring. All five compounds eluted within 3 minutes but NAT and NAB eluted very closely together. However, they were distinguished on the basis of their ion transitions, two being chosen for each TSNA, one for quantitation and one for confirmation.
Next, the TSNAs were added to tap water and extracted by SPE, which indicated that real samples did not introduce any interferences. The recoveries ranged from 70 to 97% and the method detection limits were 0.02-0.05 ng/L, depending on the particular compound.
The researchers then conducted formation potential tests, to see whether the nitrosamines could be formed in real samples in practice. They took treated water from seven drinking water treatment plants and two wastewater treatment plants and treated it with ammonia then chlorine to simulate conditions during water disinfection.
The detection of NNAL and NNN in the samples after the treatment, but not before, confirmed that they are DBPs. NNK was present before treatment but was found at much increased levels afterwards, so it can be regarded both as a DBP and a wastewater contaminant. These tests illustrated that the precursors of TSNAs are present in wastewater and have the potential to be converted.
Low loads in treated water
Having established the method and the potential for TSNAs to exist in wastewater, the researchers tested for them in the influent and effluent from drinking water treatment plants in the US and Canada. Some of them were found in the influents but only one plant contained TSNAs in the effluent.
Upon a more detailed examination, they found that the raw water from the positive effluent had a relatively high ammonia content, so much so that the added chlorine was insufficient to destroy NDMA and other TSNA precursors. However, even the total amount of NNK and NNAL in this effluent, at 0.3 ng/L, was about 200-fold lower than the amount of NDMA. This compares with a reported 10–6 cancer risk of 0.8 ng/L for TSNAs and 0.7 ng/L for NDMA.
Measures such as excess chlorine, pre-oxidation with ozone and adsorption of granular activated carbon were found to help remove the TSNA precursors. These processes are also used to remove NDMA but the researchers recommended extra studies to maximise their efficiency. The novel LC/MS method that they developed will be able to help in this as well as providing a way to assess TSNA loads in and around wastewater treatment plants.
Environmental Science and Technology 2014, 48, 1828-1834: "Identification of tobacco-specific nitrosamines as disinfection byproducts in chloraminated water"
Article by Steve Down
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.