Environmental Concentrations

Atmosphere and Precipitation

No monitoring data for DNOC in the atmosphere or precipitation in Canada were identified. Monitoring data from other countries are summarized in Table 3.

¹ ns = not specified.
² Unless otherwise specified. The range of values is indicated in square brackets, if available (e.g. ,[minimum-maximum]).

DNOC has been detected in atmospheric air and precipitation at a number of locations in Europe, and the presence of nitrated phenols in rain is not explained solely by input from pesticide applications (Leuenberger et al., 1988). DNOC has been shown to partition favourably from the gas phase into the aqueous phase, and it is not surprising that the substance has been found in rainwater (Schwarzenbach et al., 2003). DNOC was detected in Denmark, even though the substance has not been used for the last 10 years (Danish Environmental Protection Agency, 2001). The concentrations found in rain in Denmark are of the same order of magnitude as have been detected in England, Germany and Switzerland.

As no atmospheric or precipitation monitoring data for DNOC in Canada could be located, a series of release scenarios were developed to estimate the amount of DNOC that could be released into receiving waters in Canada as a result of rainfall scavenging of DNOC in the atmosphere. The scenarios incorporated precipitation data for 12 Canadian cities, an estimate of the amount of DNOC in rainwater and a calculation of runoff from built-up and natural areas into the receiving STPs. It was assumed that the rain event that would result in DNOC being removed from the atmosphere would be a heavy rainfall and that DNOC would be washed out in the early stages of the rain event and not over the length of the rainfall. The concentration of DNOC used in the scenario is based on precipitation values from Europe that were considered realistic possible levels of DNOC in air in Canada. The mean concentration of DNOC in cloudwater from northern Germany (4.2 µg/L) was selected. It was assumed that rainwater would be released as a point source from an STP, but that it would not undergo STP treatment, as STP removal efficiency during a storm event is likely to be poor. The highest concentrations of DNOC were estimated in receiving waters from the STPs in London, Ontario (0.0023 mg/L), Guelph, Ontario (0.0023 mg/L), and Granby, Quebec (0.0025 mg/L).

Aquatic Concentrations

No recent aquatic monitoring data for DNOC in Canada were identified. Older data on levels of DNOC in Canadian waters as well as in other countries are summarized in Table 4.

¹ ns = not specified; nd = not detected.
² The range of values is indicated in square brackets, if available (e.g., [minimum-maximum]).
³ Mean concentration in effluent is presented as an indication of resulting exposure. This value was not included in the section on releases of DNOC, as details on effluent quantities and release rate were not provided.

As no recent Canadian surface water monitoring data were identified, aquatic exposure estimates were modelled. The scenario uses the ChemSim model (Environment Canada, 2003c) to predict estimated exposure values. ChemSim model runs were done for three river flow estimates and two loading rates (calculated in the section on releases of DNOC), for a total of six model runs. As indicated in the release scenario, it is assumed that DNOC is in use throughout the year and that there is continuous release (24 hours per day) over the year (350 operating days). Two estimates of low river flow (2.5th and 10th percentiles) were selected to derive Estimated Exposure Values (EEVs) under low-flow conditions. The 50th-percentile flow value was also selected to estimate EEVs under more typical conditions. The maximum concentration of DNOC at 20 m downstream of the reporting facility with a worst-case scenario release of 5.7 kg/day and a 2.5th-percentile river flow is estimated to be less than 0.006 mg/L. If STP treatment is considered, an EEV of 0.0014 mg/L is estimated.

Sediment, Sewage Sludge and Soil

Monitored soil, sediment and sludge concentrations of DNOC are summarized in Table 5. The high flow and velocity of the St. Clair River rapidly dilute and disperse the substance.

Therefore, loadings of DNOC do not appear likely to cause significant exposure to benthic organisms, as only a minor amount of DNOC is expected to partition to sediments (1%). Based on the results of modelling, at a release rate of 5.7 kg/day, 0.057 kg/day (or 1%) would be available to be adsorbed onto sediments.

¹ ns = not specified; nd = not detected.
² The range of values is indicated in square brackets, if available (e.g., [minimum-maximum]).
³ <W is a qualifier, given to indicate that the sample may contain the analyte but the level would probably not exceed the laboratory method detection limit (MDL). W is approximately one-third to one-fifth of the MDL (OMEE, 1994).

DNOC was detected in 13% of Canadian municipal sludges sampled during the period 1980-1985 at concentrations ranging from 1200 to 1500 ng/g dry weight, with a median concentration of 1300 ng/g dry weight (Webber and Lesage, 1989). It was not detected (detection limit not stated) in sludge or sludge compost from various locations in Canada sampled in 1993-1994 (Webber and Nichols, 1995).

DNOC was not detected (method detection limit = 100 ng/g) in 101 samples of “rural parkland” soil or in 60 samples of “old urban parkland” soil in Ontario (OMEE, 1994). Similarly, DNOC was not detected (detection limit = 50 ng/g) in agricultural soil from various locations across Canada (Webber, 1994).

Biota

DNOC was not detected in fish composites (detection limit not stated) from the United States (DeVault, 1985).

As indicated in the section on environmental fate and partitioning, DNOC has a relatively low bioaccumulation potential. However, as will be seen in the section on effects characterization, results of repeated oral dose toxicity studies indicate that mammals may be fairly sensitive to DNOC. Therefore, wildlife exposure to DNOC from food and water has been estimated.

An EEV for wildlife was estimated based on a calculation of the total daily intake of the substance by mink and otter. An energetics model based on the general exposure model for wildlife from the U.S. Environmental Protection Agency’s (EPA) Exposure Factors Handbook (U.S. EPA, 1993) was used.

where,

TDI = total daily intake (mg/kg-bw per day)
FMR = normalized free metabolic rate of wildlife receptor of interest (250 kcal/kg-bw per day for mink and river otter)
C_i = concentration of contaminant in the ith prey species (mg/kg-bw) (see below)
P_i = proportion of the ith prey species in the diet (unitless) (default = 35% for mink; 100% for otter)
GE_i = gross energy of the ith prey species (default = 850 kcal/kg-bw prey)
AE_i = assimilation efficiency of the ith prey species by the wildlife receptor (default = 0.91)
P_t = proportion of the time

The model incorporated the metabolic rate of the wildlife receptors of interest (mink and otter), the proportion of food uptake by the receptors and the amount of time the animals spend in the contaminated area (St. Clair River), which is based on the typical habitat range of the wildlife receptors.

The concentration of the substance in a fish (Ci) must be estimated based on the highest EEVwater and a BAF. The BAF was estimated using the Modified Gobas Model (Gobas and Arnot, 2003). The BAF represents a benthic/pelagic food chain and estimates the accumulation from all sources in a mid-trophic-level fish that would typically be eaten by a mammalian piscivore.

C_i = EEV_water · BAF

where:

C_i = concentration in a prey fish (mg/kg-bw)
EEV_water = EEV calculated for surface water (mg/L) (see section on aquatic concentrations)
BAF = bioaccumulation factor for substance (L/kg) (see section on environmental fate and partitioning).
C_i = 0.0014 · 25 = 0.035

The model estimated EEVs of 0.0004 mg/kg-bw per day and 0.000 007 mg/kg-bw per day for mink and otter, respectively.