ARCHIVED - Ecological Screening Assessment for Dinitro-o-cresol (DNOC)

There are uncertainties associated with development of the ENEVs used in this assessment. However, a moderate number of empirical studies from different sources were identified, which increases confidence in the values. Application factors of 10-100 were used to account for information gaps relating to chronic toxicity, effects in the field and effects on potentially more sensitive species. Effects data were not identified for marine species.

Very few Canadian monitoring data are available for DNOC, and those that were identified were fairly old. To both support the limited amount of empirical data and provide greater insight into the potential range of levels of DNOC in the environment, releases were estimated and fate and exposure were modelled. Entry of DNOC to the environment from two sources was considered -- industrial releases and precipitation containing DNOC scavenged from the atmosphere. To address the significant uncertainty in these estimations, conservative assumptions were used to ensure that errors would be protective of the environment.

Although there have not been reports of direct releases of DNOC to water from industrial facilities, a conservative scenario was developed to estimate possible releases from an industrial source. This conservatively assumed an upper-limit estimate of the quantity of DNOC potentially used by a single facility; a slightly conservative estimate of the fraction of substance typically released due to handling practices for a substance used in bulk; and a low-percentile estimate of river flow for the receiving water body used in the scenario. Flow characteristics of the St. Clair River were used in the exposure scenario, as it is believed that the only facility in Canada currently using substantive quantities of DNOC is located near this water body. This river is extremely fast flowing and consequently disperses effluents very rapidly. Were there to be facilities having substantive releases to smaller water bodies, then the assumptions used in this scenario may not be sufficiently protective. However, it is believed that there are currently no other large users of DNOC in Canada.

Estimation of possible exposure from atmospherically generated DNOC in precipitation conservatively assumed that the concentration in the atmosphere in Canada would be similar to that in more heavily populated regions of Europe; that the rainfall event would be particularly heavy; that a high percentage of precipitation from a census subdivision would be released to the receiving river body through a single discharge point; and that there would be no removal of DNOC by the municipal STP. In particular, the assumption that atmospheric concentrations in Canada would be the same as average to high concentrations in Germany, which is much more heavily populated and industrialized, is uncertain. While it is believed that use of monitoring data from Germany in the scenario is conservative, the origins of atmospherically generated DNOC are at present not well understood, and no Canadian atmospheric monitoring data were identified for comparison.