Phytotoxicity assays with hydroxyapatite nanoparticles lead the way to recover firing range soils.

Shooting activities is an important source of Pb in contaminated soils. Lead accumulates in superficial soil horizons because of its low mobility, favouring its uptake by plants and representing a high transference risk to the trophic chain. A combination of phytoremediation with nanoremediation techniques can be used to recover firing range soils and decrease the mobility, bioavailability and toxicity of Pb. This study examines in depth the changes in Pb behaviour in firing range soils by adding hydroxyapatite nanoparticles (HANPs). These nanoparticles (NPs) may immobilise Pb and improve the quality of these areas. The use of HANPs and the Pb effects were assessed in three different species (Sinapis alba L., Lactuca sativa L. and Festuca ovina L.), focusing on their germination and early growth, through phytotoxicity assays. Single extractions with CaCl2 (0.01 M) in soils treated with HANPs show that these NPs retained Pb and reduced highly its availability and mobility. HR-TEM and TOF-SIMS were used to determine the interactions between HANPs and Pb, as well as with soil components. According to TOF-SIMS and HR-TEM/EDS analysis, Pb was mainly retained by HANPs but also associated lightly to organic matter, Fe compounds and silicates. Phytotoxicity assays exposed that S. alba, L. sativa and F. ovina were able to germinate and develop in the firing range soils despite the high available Pb contents before adding HANPs. After adding HANPs, Pb retention increased, favouring the germination and the growth of roots in the three species. These results suggest that HANPs can be used to decrease the availability and the toxicity of Pb without negative effects in the species growth. Accordingly, the combination of phytoremediation and nanoremediation techniques can be a great tool to stabilise these soils, avoiding the Pb transfer to nearby areas and its entry in the trophic chain.

Lead and PAHs contamination of an old shooting range: A case study with a holistic approach.

Soil pollution at firing ranges is an issue of growing importance, due to the accumulation in soils of contaminants derived from ammunition and clay targets. The concentration of Pb and PAHs was determined in five soils of an abandoned shooting range in Galicia (northwest Spain), and an ecotoxicological characterization was performed in order to obtain an assessment of risks. Therefore, the retention capacity of soils was assessed using test organisms of different trophic levels, and the role of soils as habitat for soil invertebrates was assessed by reproduction tests and bioaccumulation assays with earthworms. The sum of 15 PAHs ranged between 38 and 360mgkg-1, which exceed, together with Pb (160-720mgkg-1), the Galician generic reference value for urban and sporting field soils. Bioaccumulation in E. andrei showed contents up to 104,000µgPbkg-1dw, and up to 645µgPAHskg-1fw. High contents of Pb and PAHs in soil samples and in Eisenia andrei whole body, caused a reduction in the number of juveniles produced, whereas, Vibrio fischeri, Raphidocelis subcapitata and Daphnia magna displayed a slight toxic response to the soil elutriates tested. Therefore, the function of these soils to retain contaminants seemed not compromised, probably due to the high organic matter content and pH values, which are weakly acidic. The habitat function was affected, indicating that soil solution is not the only route of exposure to contaminants to E. andrei. The integration of chemical and ecotoxicological lines of evidence give rise to high risks values, restricting the use of these areas, and pointing for risks to surrounding ecosystems due to possible trophic transferences. The calculation of risks using the chemical and ecotoxicological data, required by Spanish legislation, could be a good approach to communicate with those responsible and/or involved in the management of contaminated sites.

Histopathological and molecular effects of microplastics in Eisenia andrei Bouché.

The ocean has been assumed as the main sink of microplastics (MPs), however, soils may also receive MPs from different sources and through different pathways, which may affect the biota and their role in soil functions. To the best of our knowledge, only one study, until now, reported the effects of MPs on the survival and fitness of soil organisms (Lumbricus terrestris). In our study, epigeic earthworms, of the species E. andrei, were exposed to different concentrations of MPs (0, 62.5, 125, 250, 500 and 1000 mg/kg soildw) in an OECD artificial soil and tested for reproduction, survival and growth of adults, following a standard protocol. The size of the polyethylene MPs to which earthworms were exposed ranged between 250 and 1000 µm. No significant effects were recorded on survival, number of juveniles and, in the final weight of adult earthworms after 28d of exposure, to the different concentrations of MPs. Nevertheless, FTIR-ATR of earthworms and histopathological analysis of the gut provided evidences of damages and immune system responses to MPs.

Using Ca3(PO4)2 nanoparticles to reduce metal mobility in shooting range soils.

Shooting activities are a very important source of contamination as they are commonly detected high concentrations of Pb in the soils from these facilities. Different remediation methods imply the immobilization of the pollutants by decreasing their mobility and availability and nanotechnology is a promising technique in this field. The effectiveness of calcium phosphate nanoparticles (CPNs) in the remediation of small-arms firing range and trap shooting range soils is evaluated in this work. The operationally defined extractable content of Pb, Cu and Zn is determined together with the interaction of the pollutants with the nanomaterials. Soil samples were treated with the CPNs and after the treatment the extractable contents of Cu, Pb and Zn decrease. To check the retention by the nanoparticles TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) and HR-TEM-EDS (High Resolution Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy) techniques were applied. The association of Pb and Cu to the CPNs was demonstrated by TOF-SIMS although it also indicated that not all the Pb and Cu contents are linked to the nanoparticles. By means of HR-TEM/EDS it was made out the filamentous shape and the size (50-150nm long and 20-40nm wide) of the CPNs together with their elemental composition (Ca, P and O). The CPNs were identified in treated soil samples together with signals of metals. The decrease on metal extractability detected is, in part, due to the association with CPNs but still more investigation is needed regarding mobility and availability of potentially hazardous elements in soils treated with nanoparticles.