The potential environmental toxicity of zero-valent iron nanoparticles (nZVI) and three types of nanosilver differing in average particle size from 1 to 20 nm was evaluated using seed germination tests with ryegrass, barley, and flax exposed to 0-5000 mg L(-1) nZVI or 0-100 mg L(-1) Ag. For nZVI, germination tests were conducted both in water and in two contrasting soils to test the impact of assumed differences in bioavailability of nanoparticles. Inhibitory effects were observed in aqueous suspensions at 250 mg L(-1) for nZVI and 10 mg L(-1) for Ag. Reduction in shoot growth was a more sensitive endpoint than germination percentage. Complete inhibition of germination was observed at 1000-2000 mg L(-1) for nZVI. For Ag, complete inhibition was not achieved. The presence of soil had a modest influence on toxicity, and inhibitory effects were observed at 300 mg nZVI L(-1) water in soil (equivalent to 1000 mg nZVI kg(-1) soil). Complete inhibition was observed at 750 and 1500 mg L(-1) in sandy soil for flax and ryegrass, respectively, while for barley 13% germination still occurred at 1500 mg L(-1) . In clay soil, inhibition was less pronounced. Our results indicate that nZVI at low concentrations can be used without detrimental effects on plants and thus be suitable for combined remediation where plants are involved. Silver nanoparticles inhibited seed germination at lower concentrations, but showed no clear size-dependent effects, and never completely impeded germination. Thus, seed germination tests seem less suited for estimation of environmental impact of
Although nano-sized zero-valent iron (nZVI) has been used for several years for remediation of contaminated soils and aquifers, only a limited number of studies have investigated secondary environmental effects and ecotoxicity of nZVI to soil organisms. In this study we therefore measured the ecotoxicological effects of nZVI coated with carboxymethyl cellulose on two species of earthworms, Eisenia fetida and Lumbricus rubellus, using standard OECD methods with sandy loam and artificial OECD soil. Earthworms were exposed to nZVI concentrations ranging from 0 to 2000 mg nZVI kg soil-1 added freshly to soil or aged in nonsaturated soil for 30 days prior to exposure. Regarding avoidance, weight changes and mortality, both earthworm species were significantly affected by nZVI concentrations ≥500 mg kg-1 soil. Reproduction was affected also at 100 mg nZVI kg-1. Toxicity effects of nZVI were reduced after aging with larger differences between soils compared to non-aged soils. We conclude that doses ≥500 mg nZVI kg-1 are likely to give acute adverse effects on soil organisms, and that effects on reproduction may occur at significantly lower concentrations.
Nano-scale zero-valent iron (nZVI) has been conceived for cost-efficient degradation of chlorinated pollutants in soil as an alternative to e.g permeable reactive barriers or excavation. Little is however known about its efficiency in degradation of the ubiquitous environmental pollutant DDT and its secondary effects on organisms. Here, two types of nZVI (type B made using precipitation with borohydride, and type T produced by gas phase reduction of iron oxides under H2) were compared for efficiency in degradation of DDT in water and in a historically (>45 years) contaminated soil (24 mg kg(-1) DDT). Further, the ecotoxicity of soil and water was tested on plants (barley and flax), earthworms (Eisenia fetida), ostracods (Heterocypris incongruens), and bacteria (Escherichia coli). Both types of nZVI effectively degraded DDT in water, but showed lower degradation of aged DDT in soil. Both types of nZVI had negative impact on the tested organisms, with nZVI-T giving least adverse effects. Negative effects were mostly due to oxidation of nZVI, resulting in O2 consumption and excess Fe(II) in water and soil.
Nano sized zero valent iron (nZVI) has been studied for in-situ remediation of contaminated soil 43 and ground water. However, little is known about its effects on organisms in soil and aquatic 44 ecosystems. In this study, the effect of nZVI on degradation of DDT and its ecotoxicological effects 45 on collembola (Folsomia candida) and ostracods (Heterocypris incongruens) were investigated. 46Two soils were used in suspension incubation experiments lasting for 7 and 30 days; a spiked (20 47 mg DDT kg -1 ) sandy soil and an aged (>50 yrs) DDT-polluted soil (24 mg DDT kg -1 ). These were 48 incubated with 1 or 10 g nZVI kg -1 , and residual toxicity in soil and the aqueous phase tested using 49 ecotoxicological tests with collembola or ostracods. Generally, addition of either concentration of 50 nZVI to soil led to about 50 % degradation of DDT in spiked soil at the end of 7 and 30 d incubation, 51 while the degradation of DDT was less in aged DDT-polluted soil (24 %). Severe negative effects 52 of nZVI were observed on both test organisms after 7 d incubation, but prolonged incubation led 53 to oxidation of nZVI which reduced its toxic effects on the tested organisms. On the other hand, 54DDT had significant negative effects on collembolan reproduction and ostracod development. We 55 conclude that 1g nZVI kg -1 was efficient for significant DDT degradation in spiked soil, while a 56 higher concentration was necessary for treating aged pollutants in soil. The adverse effects of nZVI 57 on tested organisms seem temporary and reduced after oxidation. 58
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