report
6.6.3 State of R&D

Unlike with groundwater, only little research has been published in the field of soil remediation. The studies on soil remediation with nanoparticles focuss mainly but not exclusively on nZVI and iron oxides (possibly catalysed by noble metals such as Pd) (Rickerby and Morrison, 2007). Challenges are the lack of data on the behavior of nanoparticles in soil, the heterogeneity of the system and concerns regarding the effect of NP-release in soil ecosystems.

nZVI

Efficient removal of polycyclic aromatic hydrocarbons (PAHs) by nZVI has been reported (Chang et al., 2007; Chang et al., 2005) while at room temperature only about 38% of the polychlorinated biphenyls (PCBs) could be reduced because of the very strong sorption of PCBs to the soil matrix (Varanasi et al., 2007). The solubility of hydrophobic organic contaminants can though be increased by polymeric nano-network particles (Tungittiplakorn et al., 2005). Satapanajaru et al. investigated the remediation of atrazine contaminated soil and found nZVI to be an effective substance for the reductive dechlorination of the pesticide (Satapanajaru et al., 2008).

nZVI was also tested as catalyst in the microbial reduction of nitrate (Shin and Cha, 2008). The authors found the combination of nZVI and biological treatment to be twice as successful as the nZVI treatment only. Other authors investigated nZVI for the remediation of atrazine-contaminated soil and water (Satapanajaru et al., 2008a).

Iron compounds

Ramsden in (Rickerby and Morrison, 2007) reports that iron oxide nanoparticles in the form of iron fillings are strong adsorbants for heavy metals in the soil. The nanoparticles with the adsorbed pollutant can then be collected using a magnetic field, and thereby eliminated from the ecosystem. These methods are yet untested on a large-scale and Ramsden doubts that iron fillings will be more effective than conventional iron scrap treatment due to the following reasons (Ramsden in (Rickerby and Morrison, 2007)): 1. The expense and environmental burden of preparing the nanoparticles; 2. Iron can be oxidized by oxygen and/or water before it has had a chance to react with the target compound and 3. The nanoparticles may in practice be agglomerated or aggregated. He further mentions the risk of introducing nanoparticles to the soil as smaller particles are much harder to confine than iron scrap.

Experiments were also conducted with nanoscale iron phosphate for the in situ immobilisation of Cu(II) (Liu and Zhao, 2007). It was shown that the bioaccessibility of Cu was reduced by 54–69% through the formation of different copper phosphate compounds.

Carbon based materials: Dendrimers, Biopolymers and Polycarbons

Dendrimers and polymers are explored for the removal of metals and organics. Xu and Zhao (Xu and Zhao, 2006) investigated the feasibility of using selected dendrimers for the removal of lead (Pb2+) from three contaminated soils. They found that lower pH increased the removal rate and that the decontamination was more effective for sandy soil than for clay soil. Around 82% of the carbonate-bound Pb2+ cations could be removed and the dendrimers as well as the Pb2+ could be recoverd to a high percentage.

Xu and Zhao (Xu and Zhao, 2006) further synthesized amphiphilic crosslinked polyurethane (ACPU) nanoparticles to wash sorbed phenanthrene from soil. They found the ACPU nanoparticles to be more effective sobents than SDS solutions.

By recombinant DNA techniques, it is now possible to create artificial nanoscale protein polymers that can be controlled precisely in terms of size, composition and thus the function. Such biopolymers are being tested as metal-binding materials for the remediation of heavy metal contaminated soil (Kostal et al., 2005).

In addition to groundwater remediation, nanotechnology holds promise in reducing the presence of NAPL. Recently, a material utilizing nano-sized oxides (mostly calcium) was used in situ to clean up heating oil spills from underground oil tanks. Preliminary results from this redox-based technology suggest faster, cheaper methods, and, ultimately, lower overall contaminant levels compared to previous remediation methods. A majority of these sites have been in New Jersey with cleanup conducted in consultation with the New Jersey Department

of Environmental Protection (http://www.continentalremediation.com/). (Karn et al., 2009)