Development of a Relative Source Contribution Factor for Drinking Water Criteria: The Case of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)

Abstract

The consideration of multiple or cumulative sources of exposure to a chemical is important for adequately protecting human health. This assessment demonstrates one way to consider multiple or cumulative sources through the development of a relative source contribution (RSC) factor for the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), using the Exposure Decision Tree approach (subtraction method) recommended by the U.S. Environmental Protection Agency. The RSC factor is used to ensure that the concentration of a chemical allowed by a regulatory criterion or multiple criteria, when combined with other identified sources of exposure common to the population of concern, will not result in unacceptable exposures. An exposure model was used to identify relevant potential sources for receptors. Potential exposure pathways include ingestion of soil, water, contaminated local crops and fish, and dermal contact with soil and water. These pathways are applicable only to areas that are in close proximity to current or former military bases where RDX may have been released into the environment. Given the physical/chemical properties and the available environmental occurrence data on RDX, there are adequate data to support a chemical-specific RSC factor for RDX of 50% for drinking water ingestion.

Final Report: Applying a tested procedure for the identification of potential emerging chemical risks in the food chain to the substances registered under REACH ‐ REACH 2

“…Fish, meat & milk products, fruits and vegetables, grass (Score C = 10 in all items) * ENV: Environmental occurrence (in water, soil etc. ); FOOD: Occurrence in food or feed ** Dossier: REACH registration dossier *** MAN: Manufacture, FORM: Formulation, IND: Industrial uses, PROF: Professional uses, CONS: Consumer use, ASL: Article service life § Food/feed items with a Score C of 6 or 10 based on ACC-HUMANsteady modelling Name/synonyms : Hexahydro-1,3,5-trinitro-1,3,5- Reviews (ATSDR, 2012; NLM, 2018a) Concentrations measured: untreated wastewater from RDXmanufacturing plant (presumably USA): 3.28 mg/L (N=1); groundwater at former ammunition sites in Lower Saxony (Germany): 21 µg/L and in Saxony (Germany): 2.4 mg/L (N=1 for each) RDX detection frequency and concentration range at 34 US Department of Defence sites: groundwater (12/34; <LoD-36 mg/L), surface water (3/34; >0.004-109 mg/L), soil (22/34; <Lod-13 900 mg/kg), sediment (6/34; 2-120 000 mg/kg) Literature (Godejohann et al, 1998;Gadagbui et al, 2012;Shi et al, 2015) Concentrations in Swiss lakes: AM: 0.2, MAX: 0.81 ng/L (Lake Thun and Lake Brienz); AM: 7.24, MAX: 15 ng/L (Lake Lucerne); all samples in sediment <LoD; occurrence related to external sources (e.g. sites manufacturing explosives, former military sites, tunnel construction/mining) rather than to munitions dumped in the three lakes (containing about 78 kg RDX)…”

“…in alfalfa, spinach shoots and lettuce leaves, lower values e.g. in tomato fruit, bush bean fruit and bean roots Reviews (McKone and Maddalena, 2007;Gadagbui et al, 2009) Mean BCF (shoot) in rye grass (Lolium perenne) 71.8 (range (N=3): 19. 2-108.3; BCF values appeared to be inversely related with RDX concentrations in soil (range: 10-154 mg/kg dw.…”

“…in alfalfa, spinach shoots and lettuce leaves, lower values e.g. in tomato fruit, bush bean fruit and bean roots Reviews (McKone and Maddalena, 2007;Gadagbui et al, 2009) EFSA Supporting publication 2019:EN-1597 Mean BCF (shoot) in rye grass (Lolium perenne) 71.8 (range (N=3): 19.2-108.3; BCF values appeared to be inversely related with RDX concentrations in soil (range: 10-154 mg/kg dw. ); similar results in additional tests with the same species (BCF (shoot): AM: 17, range 2-58), and with alfalfa (Medicago sativa; BCF (shoot): AM: 37, range 3-134) ; in both species, highest BCF at lowest concentration in soil (14 mg/kg dw.…”

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) causes seizure activity in larval zebrafish via antagonism of γ-aminobutyric acid type A receptor α1β2γ2

“…Hexahydro-1,3,5-trinitro-1,3,5-triazine, or Royal Demolition Explosive (RDX) is a common component of plasticized explosives, such as C-4, used extensively by militaries worldwide. RDX is also a persistent environmental contaminant found in soil, air, and groundwater surrounding military sites (Gadagbui et al 2012 ). It is released via munitions use and from waste generated during its manufacture, packaging, or disposal.…”

The Use of Exposure Source Allocation Factor in The Risk Assessment of Drinking-Water Contaminants

“…In the subtraction method, the contributions of the sources of exposure other than drinking water and fish are subtracted from the RfD, thus reducing the amount available to be allocated to develop water-related guideline values. In essence, then, the contribution of exposure source(s) other than the source of concern to the intake value is subtracted out (U.S. EPA, 2000; Gadagbui et al, 2012). This procedure is applicable for pollutants for which only one criterion or standard is available, since it involves subtracting out the contribution of other exposure sources from the intake value or a criterion for one specific medium (e.g., consideration of fish consumption in establishing drinking water guidelines).…”