Molecular signature of organic nitrogen in septic-impacted groundwater

Abstract

27Dissolved inorganic and organic nitrogen levels are elevated in aquatic systems due to 28 anthropogenic activities. Dissolved organic nitrogen (DON) arises from various sources, and its 29 impact could be more clearly constrained if specific sources were identified and if the molecular-30 level composition of DON were better understood. In this work, the pharmaceutical 31 carbamazepine was used to identify septic-impacted groundwater in a coastal watershed. Using 32 ultrahigh resolution mass spectrometry data, the nitrogen-containing features of the dissolved 33 organic matter in septic-impacted and non-impacted samples were compared. The septic-34 impacted groundwater samples have a larger abundance of nitrogen-containing formulas. 35Impacted samples have additional DON features in the regions ascribed as 'protein-like ' and 36 'lipid-like' in van Krevelen space and have more intense nitrogen-containing features in a 37 specific region of a carbon versus mass plot. These features are potential indicators of dissolved 38 organic nitrogen arising from septic effluents, and this work suggests that ultrahigh resolution 39 mass spectrometry is a valuable tool to identify and characterize sources of DON. 40 41Introduction 42 Groundwater is an important source of freshwater to coastal systems.1, 2 Thus, 43groundwater is a source of nitrogen to coastal waters, especially if it has been impacted by 44 human activities. Dissolved nitrogen is comprised of both inorganic (nitrate, nitrite, and 45 ammonia) and organic forms. The quantitative balance between inorganic and organic nitrogen 46 will depend on various factors, including sources and biological activity, but evidence suggests 47 that dissolved organic nitrogen (DON) can be quantitatively as important as inorganic forms of 48 nitrogen in groundwater.3 For example, Kroeger et al. 3 found that DON comprised 10-93% of 49 total dissolved nitrogen in a set of coastal watersheds. Both the source and environmental 50 conditions influence the bioavailability and processing of DON, with bioavailability ranging 51 from 1-60%.4, 5 Sources of DON include precipitation, agriculture, natural runoff/infiltration, 52 artificial recharge of wastewater, and septic systems. In populated coastal areas, septic systems 53 may be particularly important sources of both inorganic and organic nitrogen.3, 6-8 At present, 54however, it is difficult to link the bulk DON found in impacted aquatic systems to specific 55 sources or processes due to a lack of information about the molecular-level composition of DON. 56 3 Information regarding the molecular-level composition of DON is important to 57 improving understanding the reactivity of the pool of nitrogen in aquatic systems. studies have found such compounds in impacted groundwater, which also serves as the drinking 82 water source for the population.27, 28 Some of these compounds, including carbamazepine (an 83 anti-convulsant) and artificial sweeteners, appear to be persistent and sorb to soils or sediments 84 only to a limi...

The effect of advanced secondary municipal wastewater treatment on the molecular composition of dissolved organic matter

“…In contrast, N-containing formulas could not be assigned to any peaks observed using negative ESI FT-ICR MS in primary or secondary effluent (Tseng et al, 2013). While compounds with amine functional groups should ionize well in positive mode (Arnold et al, 2014), the interpretation of positive mode ESI spectra is complicated by the presence of sodium adducts (Koch et al, 2005); this challenge may explain why positive mode ESI data of wastewater-related samples has not been previously reported. To address this issue, both [M+H] + and [M+Na] + ions were considered for the assignment of CHON formulas (Koch et al, 2005) and only formulas that were part of a +CH 2 or (+CH 4 – O) homologous series were considered (Koch et al, 2007; Kujawinski and Behn, 2006).…”

“…Similarly, negative mode CHON formulas in the protein-like (i.e., aliphatic) and lignin-like regions were found in tertiary wastewater effluent (Mesfioui et al, 2012) and DOM derived from the sludge of continuously-stirred tank biogas reactors (Shakeri Yekta et al, 2012), which also contains protein-derived compounds of human and microbial origin. Although positive mode CHON formulas have not been previously reported in wastewater, they have been identified in septic-impacted groundwater using FT-ICR MS (Arnold et al, 2014). The CHON formulas in the septic-impacted samples were found in the lipid- and protein-like regions, in agreement with the Nine Springs samples.…”

Environmental metabolomics: Analytical strategies

“…Solid phase extraction with PPL is in fact, currently the most popular choice for highthroughput isolation of DOM (Arnold et al, 2014;Flerus et al, 2012;Lawson et al, 2014;Roth et al, 2013). We have chosen PPL for extracellular metabolite extraction so that the LC-MS metabolomics data sets from our field and laboratory samples are comparable, and so that they can dovetail with other DOM measurements.…”

The Impact of Landscape Characteristics on Groundwater Dissolved Organic Nitrogen: Insights From Machine Learning Methods and Sensitivity Analysis

“…Kroeger et al () reported a positive correlation between groundwater DON concentrations and population density. Arnold et al () analyzed the molecular‐level composition of groundwater DON to demonstrate that septic systems were a dominant source of DON. However, others have reported that DON is predominantly derived from natural sources.…”