Environmental and Analytical Chemistry Session Track Highlights
Erik Smolders, Katholieke Universiteit Leuven, Belgium
As I said in Milan, chemistry has never been the principal focus at SETAC, but it is critical because environmental toxicology and risk assessment all starts with chemical reactions that determine fate, and hence, the dose of the chemical. When you look at it by the numbers, chemistry was seemingly well represented in Milan. Of the 88 regular platform sessions, 18 were on the environmental and analytical chemistry track. In addition, there were four sessions on emerging pollutants; five on handling, monitoring, and remediation of pollution; seven on nanomaterials and nanoparticles; and two on QSARs and exposure modeling. Among the six special sessions were sessions on emerging exposure science and new QSAR modeling. So, after accounting for these “allied tracks,” at least 38 out of 94 sessions in Milan were about environmental and analytical chemistry.
Despite some very interesting presentations, it was a little bit disappointing, though, that chemistry often does not deserve the bare minimum in studies. For example many reported studies still rely on nominal concentrations rather than confirming actual concentrations. In addition processes that substantially affect bioavailability (e.g., sorption, speciation, complexation) are often ignored.
The nanomaterials and nanoparticles sessions included some good, interesting chemistry. If you attended those sessions, you learned that nanoparticles research is a lot about chemistry. What is their fate, what makes them available at the site of uptake? We need to understand the chemistry and environmental fate of nanoparticles before we can predict their toxicity in the environment and estimate the risks.
We are on our way to being able to measure nanoparticles in the environment at realistic concentrations. We are not there yet. For example, we still need quality control programs, and we need to scale up the technology, but we’re getting there. The technique we’ll be hearing about more and more is FFF-SP-ICP-MS. Field flow fractionation uses hydrodynamic forces to size sort nanomaterials. Single particle ICP-MS is a technique for detecting, and semi-quantitatively sizing, single nanoparticles. FFF-SP-ICP-MS is not without its problems—all analytical techniques have problems—but there seems to be a growing consensus that this is the way to go for analyzing nanoparticles. As an example, Hassellöv and Cornelis (NM01A-3) gave a presentation on the use of FFF-SP-ICP-MS to detect manufactured nanoparticles from winter tire studs in highway runoff.
Other interesting presentations in the nanomaterials and nanoparticles sessions dealt with the question of nanoparticles aggregation and dissolution. Heithmar (NM01B-5) gave a nice presentation on particle size, concentration, and salinity dependence of silver nanoparticle aggregation and dissolution. We learned that at lower concentrations they dissolve more and at higher concentrations they flocculate more, and that all these things are apparently more pronounced in saline water than in freshwater. Galceran (NMO1B-1) gave a presentation on zinc oxides, confirming with the speciation measurement that zinc oxide nanoparticles dissolve quite rapidly in water. On a topic relating toxicity to chemistry, many groups have found good, reproducible and relatively realistic ways to add nanoparticles to soil. Kool et al. (NM02C-5) compared soil dissolution and solubility of “nano” and “non-nano” zinc oxides. What they found was that zinc solubility in filtered pore water was the same for nano and non-nano particles, and that nano and non-nano zinc oxide particles have the same toxicological effects.
Microextraction techniques for persistent organic pollutants (POPs) and pharmaceuticals and personal care products (PPCPs) received a lot of attention in Milan. These are techniques for concentrating very low environmental concentrations. They include solid phase microextraction (SPME) and hollow fiber microextraction (HFME) techniques. Nice work was presented on calibrating microextraction instruments to accurately measure not just environmental concentrations but also to predict bioaccumulation.
Other POPs and PPCPs presentations focused on the details of what controls the rate of uptake in passive samplers. Understanding uptake sometimes requires understanding complicated diffusion equations but not always. For example a talk by Weiss et al. in the session on Advances in Passive Sampling and Dosing Techniques (EC01A) showed that sometimes a passive sampler is just what you eat in your sandwich. The investigators collected 160 butter samples from around Europe, analyzed them for POPs, and found a beautiful correlation between POPs in butter and air concentrations of these POPs.
Passive dosing is the reverse of passive sampling. In the laboratory, it’s possible to use materials containing POPs to release very low (ng/L) hydrophobic contaminant concentrations into solution, enabling us to study fate and effects at environmentally relevant concentrations. One nice example was work by Smith et al. (EC01D-6a) that used passive dosing to investigate the degradation of phenanthrene at environmentally relevant concentrations.
Something new on sorption was presented by Pignatello et al. (HM04-5). There has been a lot of attention paid to using activated carbon to amend soils and sediments to increase binding and thereby remediate them. There is interest of course in understanding the activated carbon binding mechanism. Phenols, which often negatively charged at ambient pH, should be highly soluble according to conventional partitioning theory. Surprisingly, though, on activated carbon they are highly sorbed. The binding mechanism is revealed in the Pignatello group’s presentation. Another interesting, “good news” finding on activated carbon was presented by Marchal (HM04-2). In that presentation it was reported that adding activated carbon to reduce PAH mobility in soil does not decrease its biodegradation and mineralization despite higher sorption.
Finally, getting to metals and metalloids, you are probably aware of the biotic ligand model (BLM), which takes into account metals speciation and complexation in predicting toxicity. Complexed metals generally are not bioavailable; it is the free ions that we are worried about. One of the interesting results reported at this conference concerning metals bioavailability was a finding by Kilgore et al. (ET12A-2) of appreciable concentrations of lipophilic copper complexes in natural waters, which was a bit surprising. We know from studies of manufactured lipophilic metals compounds that they are often neutral compounds, readily able to cross cell membranes, and therefore highly bioavailable. Whether the same is true of these lipophilic compounds detected in natural waters and what it means in terms of environmental risks, is far from clear. This is just a first step, but this is a question that deserves further attention.
As a closing note, the consideration of metal speciation is increasingly being incorporated into environmental regulations both in the EU and elsewhere. With metals, we know for sure that total concentrations are not good predictors of risk. A lot of progress was made toward establishing this over the last ten years. This is an area where chemistry really bridged well with the whole bioavailability and risk side of things. There was a lot of work presented in the metals and metalloids session on science in support of regulatory development, and it was nice to see chemistry in action in risk assessment and regulation.
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