This week’s Spinneret post actually points you to my latest Alchemist column on ChemWeb.com but also goes into a little more detail on one of the items reported there regarding pesticide contamination.
First off, Environmental research gets a boost from NIH in the form of a $6.8million grant to establish three DISCOVER centers to study the effects of environmental pollutants. Crystallography reveals the cellular machinations of the humble hydrogen peroxide molecule in The Alchemist this week, while fatty samples suggest that all of us harbor at least one pesticide or other persistent organic compound in our tissues. In environmental news, researchers have turned to gold to help them convert biomass into a useful chemical feedstock, while in theoretical studies it still matters, relatively, that electrons and nuclei are massively and speedily different. Finally, crystals behaving badly in supramolecular chemistry could herald new approaches to technological problems.
Read current issue of The Alchemist here.
Anyway, back to the contentious item on global contamination, which referred to news that almost everyone in Spain, and putatively the world, may be contaminated with at least one pesticide. I did have some misgivings about reporting on this and my concerns were brought into sharp relief by an Alchemist reader friend who happens to be a retired organic chemist with a great deal of experience.
He points out that the item on finding persistent organics in blood serum should really be put into perspective. “The fact that many of these studies find mainly halogenated compounds may well simply reflect the exquisite sensitivity of the detectors used in capillary gas chromatography to halogen,” he says, “these devices will pick up nanomolar concentrations of compounds containing chlorine or bromine.” He also asks whether strict controls were used by the investigators in this research and points out that work in this area submitted for regulatory filing requires stringent controls beyond simply showing a peak that has roughly the same Rf as a suspected pollutant.
More to the point, however, he questions the significance of finding traces of DDT or even DDE in serum. “If this were truly perilous the landscape should be littered with victims,” he says.
Follow-up comment via email from Dan Lednicer whose original email inspired this post:
My comments reflected the four years that I worked in a contract analytical firm rather than personal criticism. A good many of our contracts involved determination of levels of drugs in serum samples from clinical trials. Since the data were intended to support the New Drug Application to be filed with FDA analyses were carried out with exceedingly stringent operating procedures.
A typical day’s run was preceded by determination of a calibration curves, this comprised injection of seven samples extracted from spiked serum samples in exactly the same manner as samples from the trial. (If this did not yield a correlation coefficient of .995, it was back to the drawing board). Samples of spiked with known concentrations of drug were randomly interspersed among real samples when it came time for the actual analytical work so that no more than five consecutive shots consisted of unknowns.
Many of the assays we carried out were linear down to the level for nanograms/mL. Though we could sometimes see even lower levels those data could not be used as they were beyond the linear range. Preparation of pefluorinated derivatives (i.e. heptafluorobutyric ester or amide) not only increased detector sensitivity but also increased ‘??volatility’, lowering retention time.
Much the same protocol applied to HPLC assays, though in this case sensitivity to halogen did not apply.
Dan