Accumulation of Insensitive Munition Compounds in the Earthworm Eisenia andrei from Amended Soil: Methodological Considerations for Determination of Bioaccumulation Factors.

The present study investigates the bioaccumulation of the insensitive munition compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), developed for future weapons systems to replace current munitions containing sensitive explosives. The earthworm Eisenia andrei was exposed to sublethal concentrations of DNAN or NTO amended in Sassafras sandy loam. Chemical analysis indicated that 2- and 4-amino-nitroanisole (2-ANAN and 4-ANAN, respectively) were formed in DNAN-amended soils. The SumDNAN (sum of DNAN, 2-ANAN, and 4-ANAN concentrations) in soil decreased by 40% during the 14-d exposure period. The SumDNAN in the earthworm body residue increased until day 3 and decreased thereafter. Between days 3 and 14, there was a 73% decrease in tissue uptake that was greater than the 23% decrease in the soil concentration, suggesting that the bioavailable fraction may have decreased over time. By day 14, the DNAN concentration accounted for only 45% of the SumDNAN soil concentration, indicating substantial DNAN transformation in the presence of earthworms. The highest bioaccumulation factor (BAF; the tissue-to-soil concentration ratio) was 6.2 ± 1.0 kg/kg (dry wt) on day 3 and decreased to 3.8 ± 0.8 kg/kg by day 14. Kinetic studies indicated a BAF of 2.3 kg/kg, based on the earthworm DNAN uptake rate of 2.0 ± 0.24 kg/kg/d, compared with the SumDNAN elimination rate of 0.87 d-1 (half-life = 0.79 d). The compound DNAN has a similar potential to bioaccumulate from soil compared with trinitrotoluene. The NTO concentration in amended soil decreased by 57% from the initial concentration (837 mg NTO/kg dry soil) during 14 d, likely due to the formation of unknown transformation products. The bioaccumulation of NTO was negligible (BAF ≤ 0.018 kg/kg dry wt). Environ Toxicol Chem 2021;40:1713-1725. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Biomonitoring and assessment of monomethylmercury exposure in aqueous systems using the DGT technique.

A series of laboratory experiments was conducted under realistic environmental conditions to test the ability of the Diffusive Gradient in Thin film (DGT) technique to mimic monomethylmercury (MMHg) bioaccumulation by a clam (Macoma balthica, Baltic clam). Using isotope enriched MMHg as tracers, bioavailability was determined by comparing the rate of MMHg uptake by novel DGT devices and sentinel organism over time. Experiments were conducted under varying conditions of salinity and MMHg speciation. Depending on MMHg level and speciation in the dissolved phase, MMHg uptake rates by the sentinel organism varied greatly from 0.4 to 2.4Lg(-1)d(-1). Reproducibilities of MMHg uptakes by DGT and clams were estimated at 7 and 38%, respectively. A significant linear relationship (log basis) between MMHg accumulation by DGT and clams was observed (r(2)=0.89). The study demonstrates that DGT results reasonably predict MMHg uptake by clams from the aqueous phase and provide the basis for application of the DGT device as a surrogate for sentinel organism for monitoring bioavailable MMHg.

Benthic bioaccumulation and bioavailability of polybrominated diphenyl ethers from surficial Lake Ontario sediments near Rochester, New York, USA.

Polybrominated diphenyl ethers in Lake Ontario watershed sediments were assessed for benthic bioavailability through the use of biota-sediment accumulation factors. Sediments from lake and Rochester Harbor (lower Genesee River) areas were investigated. Congeners 47, 66, 85, 99 and 100 were detected in tissues of the oligochaete Lumbriculus variegatus. Biota-sediment accumulation factors ranged from 3.95 (congener 154) to 19.5 (congener 28) and were higher at the Lake Ontario area. The lower biota-sediment accumulation factors for the Rochester Harbor sediment may result from a higher fraction of black carbon generally expected in highly urbanized rivers. Degree of bromination may reduce bioavailability.

Bioaccumulation of TNT and DDT in sheepshead minnows, Cyprinodon variegatus L., following feeding of contaminated invertebrates.

The aim of this study was to determine the potential for dietary uptake by trophic transfer using the explosive 2,4,6-trinitrotoluene (TNT) and the substantially more hydrophobic dichlorodiphenyltrichloroethane (DDT) utilizing the amphipods Leptocheirus plumulosus as prey and the fish Cyprinodon variegatus as predator. Bioaccumulation did not change significantly over time for TNT but apparent steady-state was not reached for DDT at exposure termination after 7 days of dietary exposure. The bioaccumulation factor was 0.09 mg/mg for TNT and 0.34 mg/mg for DDT, confirming the low potential of TNT to bioaccumulate in fish.

Comparative toxicokinetics of explosive compounds in sheepshead minnows.

Juvenile sheepshead minnows Cyprinodon variegatus were exposed to the explosive compounds 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and to the TNT transformation products 2-aminodinitrotoluene (2-ADNT) and 2,4-diaminonitrotoluene (2,4-DANT) in five separate water-only experiments. A one-compartment model was used to characterize uptake (k(u)) and elimination (k(e)) rate constants and to estimate bioconcentration factors (BCFs). The compounds investigated in this study are weakly hydrophobic. Kinetically derived BCFs (9.6, 13.1, 0.5, 1.7, and 0.5 ml g(-1) for TNT, 2-ADNT, 2,4-DANT, RDX, and HMX, respectively) confirmed the expected low bioaccumulative potential of those compounds and the positive relationship between log BCF and log K(ow) (1.6, 2.0, 0.8, 0.9, and 0.2 for TNT, 2-ADNT, 2,4-DANT, RDX, and HMX, respectively). The uptake clearance (k(u)) was relatively slow for all compounds (7.3, 12.6, 1.3, 0.15, and 0.06 ml g(-1)h(-1) for TNT, 2-ADNT, 2,4-DANT, RDX, and HMX, respectively), and overall, it decreased with decreasing compound hydrophobicity. Elimination was extremely fast for the nitroaromatic compounds (0.77, 0.96, and 2.74 h(-1) for TNT, 2-ADNT, and 2,4-DANT, respectively), thus resulting in very short biological half-lives (<1 hour), but it was much slower for the cyclonitramines (0.09 h(-1) for RDX and 0.12 h(-1) for HMX). Although ADNTs were present in fish exposed to TNT, the parent compound was the dominant compound in tissues during the uptake and elimination exposures. The rates of metabolite formation (0.06 h(-1)) and elimination (0.16 h(-1)) were much slower than the rate of elimination of the parent compound (0.80 h(-1)). Because of the fast elimination rate of TNT and its transformation products and the exceedingly low bioaccumulative potential of RDX and HMX, exposure conditions likely associated with the presence of explosives in aquatic systems are unlikely to pose unacceptable risks to fish.

Toxicity of sediment-associated nitroaromatic and cyclonitramine compounds to benthic invertebrates.

The toxicity of nitroaromatic (2,4-diaminonitrotoluene [2,4-DANT] and 1,3,5-trinitrobenzene [TNB]) and 14C-labeled cyclonitramine compounds (hexahydro-1,3,5-trinitro-1,3,5-triazine [RDX] and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine [HMX]) to the marine polychaete Neanthes arenaceodentata and the estuarine amphipod Leptocheirus plumulosus following 10- or 28-d exposures to spiked sediments was investigated. Organismal-level effects on survival, growth, and reproduction and cellular-level effects on apoptosis (programmed cell death) were evaluated. Because cyclonitramines have low affinity for sediment, overlying water was not exchanged in the RDX and HMX exposures. Nitroaromatics sorbed strongly to sediment, resulting in near complete resistance to solvent extraction. Cyclonitramines sorbed weakly to sediment, as more 14C-activity was found in the overlying water than in the sediment at exposure termination. No significant decrease in survival or growth was observed with cyclonitramines at initial sediment concentrations as high as 1,000 microg/g. Survival was significantly affected by nitroaromatics at nominal sediment concentrations as low as 200 microg/g, with L. plumulosus being more sensitive than N. arenaceodentata. Growth was significantly decreased at sublethal concentrations of 2,4-DANT for N. arenaceodentata. Reproduction, measured only with L. plumulosus, was significantly decreased only in the highest RDX treatment and also in the lower TNB treatment. However, no decrease was observed in higher concentrations of TNB. Body burden at exposure termination was below detection limit (1 microg/kg) for all compounds. Significant inhibition of apoptosis was not accompanied by significant decreases in growth or reproduction. Because of its critical function in many biological processes. alterations in this endpoint may result in adverse effects on the organism and could be used as an early indicator of toxicity.

DDT toxicity and critical body residue in the amphipod Leptocheirus plumulosus in exposures to spiked sediment.

The lethal and sublethal toxicity of dichlorodiphenyltrichloroethane (DDT) to the estuarine amphipod Leptocheirus plumulosus was determined using sediment spiked with (14)C-labeled compound. Juvenile amphipods were exposed to concentrations up to 9.9 nmol/g dry weight (3.5 microg/g). Acute effects on survival were determined in a 10-day experiment. Chronic effects on survival, growth, and reproduction were assessed in a 28-day experiment. The DDT in the sediments transformed to dichlorodiphenyldichloroethane (DDD), dichlorodiphenyldichloroethylene (DDE), and polar metabolites during the 14-day sediment storage prior to exposing the amphipods. The mixture of DDT and its breakdown products (tDDT) was comprised mostly of DDT at the beginning of the exposures. DDD was the prevalent compound at termination of the 28-day exposure. Complete mortality occurred at sediment concentrations of tDDT as low as 7 nmol/g (2.3 microg/g) in both acute and chronic experiments. Most of the mortality appeared to have occurred within the first 4 days of exposure. No sublethal reductions in growth or reproduction were observed in the 28-day experiment. In the 10-day experiment, where amphipods did not receive supplemental food, growth was significantly increased in DDT treatments where survival was not affected. The concentration of tDDT in amphipod tissues was determined at exposure termination. In the 10-day experiment, a mean body residue of 14 nmol/g wet weight was associated with significant mortality (30%). Lower critical body residues were observed in the 28-day experiment, where the median lethal tissue residue (LR(50)) was 7.6 (6.8--8.4, 95% confidence interval) nmol/g wet weight. Based on previous studies, the lethal critical body residue for L. plumulosus is similar to those determined for freshwater amphipods and substantially lower than those determined for cladocerans and polychaetes.

Toxicity and bioaccumulation of DDT in freshwater amphipods in exposures to spiked sediments.

The amphipods Hyalella azteca and Diporeia spp. were exposed to sediments dosed with dichlorodiphenyltrichloroethane (DDT), and the toxicity and toxicokinetics were determined. The toxicity was evaluated with the equilibrium partitioning (EqP) and critical body residue approaches. The DDT in the sediments degraded during the equilibration period prior to organism exposure. Thus, the toxicity using EqP pore-water toxic units (TUs) was evaluated for DDT and its degradation product, dichlorodiphenyldichloroethane (DDD), as the ratio of the predicted interstitial water concentration divided by the water-only LC50 values. The sum of TUs (sum(TU)) was assumed to best represent the toxicity of the mixture. For H. azteca, the 10-d LC50 was 0.98 and 0.33 sum(TU) for two experiments. For Diporeia spp., no toxicity was found in the first experiment with up to 3 sum(TU) predicted in the interstitial water. However, in the second experiment, the 28-d LC50 was 0.67 sum(TU). These data suggest that the EqP approach approximately predicts the toxicity for the combination of DDT and DDD in sediment, provided a toxic unit approach is employed. The critical body residue approach also used TUs because DDT is biotransformed by H. azteca and because of the dual exposure to DDT and DDD. Because biotransformation was only determined in the second experiment, the critical body residue approach could only be evaluated for that case. The TUs were calculated as the ratio of the concentration in the live amphipods divided by the respective LR50 (residue concentration required to produce 50% mortality) values. The LR50 was 1.1 sum(TU) for H. azteca for the 10-d exposure and 0.53 for Diporeia spp. after a 28-d exposure. Thus, this approach was also quite successful in predicting the toxicity. The accumulation and loss rates for H. azteca were much greater than for Diporeia spp. Thus, 10-d exposures represent steady-state conditions for H. azteca, while even at 28-d, the Diporeia spp. are not at steady state.