Effects, transfer, and fate of RDX from aged soil in plants and worms

Abstract

The objectives of this study were to provide data that can be used to predict exposure-based effects of RDX in aged soil on multiple endpoint organisms representing two trophic levels. These data can be used for defining criteria or reference values for environmental management and conducting specific risk assessment. Dose-response experiments formed the basis for the evaluation of toxic effects and transfer of contaminants from soil into two trophic levels. Long-term exposure tests were conducted to evaluate chronic, sublethal, toxicity and transfer of aged soil-based explosives, with RDX as main contaminant. In these tests, plants were exposed for 55 days in the greenhouse, biomass was determined and residues of explosives parent compounds and RDX metabolites were analyzed using HPLC techniques. Worms were exposed for 28 days (Eisenia fetida) and 42 days (Enchytraeus crypticus) in the laboratory, biomass and number were determined, and tissues were analyzed for explosives compounds. The plants tolerated concentrations up to 1540 mg RDX kg À1 soil-DW. Biomass of Lolium perenne was not significantly related to soil-RDX concentration, while biomass of Medicago sativa significantly increased. No screening benchmark for RDX in soil for plants was calculated, since concentrations up to 1540 mg kg À1 soil failed to reduce biomass by 20% as required for a LOEC. RDX, RDX-metabolite MNX, and accompanying HMX concentrations in plants were significantly related to concentrations in soil after 55 days of exposure (RDX: R 2 = 0.77-0.89; MNX R 2 = 0.53-0.77; HMX: R 2 = 0.67-0.71). The average bioconcentration factors (BCF) were for RDX 17 in L. perenne and 37 in M. sativa, and for HMX 2 in L. perenne and 44 in M. sativa. The worms also tolerated concentrations up to 1540 mg RDX kg À1 soil-DW. Biomass of E. fetida adults decreased with soil-RDX concentration, and a LOEC of 1253 mg kg À1 soil-DW was estimated. RDX concentrations in E. fetida were significantly related to concentrations in soil after 28-day exposure (R 2 = 0.88). The average BCF in E. fetida for RDX was 1. Because in response to exposure to RDX-contaminated soil the RDX concentrations in plants increased initially and decreased subsequently, while those in worms increased continuously, RDX in worm tissues may accumulate to higher concentrations than in plant tissues, regardless of the low average BCF for worms.

Role of soil interstitial water in the accumulation of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine in the earthworm Eisenia andrei

“…The biota-soilaccumulation factor (BSAF), typically expressed as the ratio of tissue to total soil concentrations [19], is often used to characterize the bioaccumulation potential of a chemical from soil to a soil-dwelling organism, such as the earthworm. Recent studies have shown, however, that the BSAF of RDX in earthworms decreased from 6.7 to 0.10 g soil/g tissue as the RDX concentration in soil increased from 1 to 10,000 mg/kg soil [1,15,16]. A varying BSAF value can increase the uncertainty of estimated food chain transfer potential for RDX during the ecological risk assessment at a contaminated site.…”

“…Previous experiments demonstrated a limited accumulation potential for RDX in earthworms [1,[15][16][17], as could be expected from its low log K OW of 0.87 [18]. The biota-soilaccumulation factor (BSAF), typically expressed as the ratio of tissue to total soil concentrations [19], is often used to characterize the bioaccumulation potential of a chemical from soil to a soil-dwelling organism, such as the earthworm.…”

“…The RDX concentrations can range from very low levels to 3,500 mg/kg at some military firing and training sites and can reach up to 74,000 mg/kg at open burning/open detonation areas [1][2][3][4][5][6].…”

“…The U.S. Environmental Protection Agency (U.S. EPA) Method 8330A [20] (http://www.epa.gov/waste/hazard/ testmethods/sw846/online/8_series.htm) is often used in ecotoxicity studies to estimate the RDX exposure concentration in soil [1,15,16]. This method, which is based on acetonitrile extraction, quantifies the total concentration of RDX that includes the nonsoluble (crystalline plus sorbed) and the water-soluble fractions of RDX.…”

Fate of CL-20 in sandy soils: Degradation products as potential markers of natural attenuation

“…The manufacturing and usage of munitions has resulted in severe contamination of both soils and groundwater (Pennington and Brannon, 2002;Best et al, 2006). Toxicological studies showed that CL-20 did not adversely affect terrestrial plants and indigenous soil microorganisms but was highly toxic to the earthworm Eisenia andrei and potworms Enchytraeus crypticus and Enchytraeus albidus (Dodard et al, 2005;Kuperman et al, 2006).…”