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July 19th, 2011

Rietveld X-ray analysis helps REACH chemical assessment grouping, fewer tests

Published on July 19th, 2011 | By: Eileen De Guire

Grouping of substances can expedite EU REACH compliance.

In late 2006, the European Union passed the legislation known as REACH (Registration, Evaluation, Authorization and Restriction of Chemicals), which became effective on June 1, 2007. The legislation extends globally to any manufacturer or supplier wanting to do business in the EU.

The European Chemicals Agency has issued many documents to provide compliance guidance (available on the ECHA website). Chemicals and raw materials that fall under REACH authority are subject to chemical safety assessment, which includes solubility testing and possibly animal testing. A May 2008 ECHA document provides guidance on approaches to meeting the toxicity requirements that outlines non-testing approaches to compliance for the purpose of minimizing animal testing. The concept is to implement QSARs (quantitative structure-activity relationships) and grouping of substances.

(The UK’s Health and Safety Executive also has useful information on REACH requirements and compliance.)

ECHA defines a QSAR as a “mathematical model (often a statistical correlation) relating one or more quantitative parameters derived from chemical structure to a quantitative measure of a property or activity…. QSARs are quantitative models yielding a continuous or categorical result.” It goes on, “The most common techniques for developing QSARs are regression analysis, neural nets and classification methods.”

A new paper in the July/August issue of the International Journal of Applied Ceramic Technology summarizes an approach using the Rietveld method of X-ray diffraction to grouping differing pigment formulations together. (The Rietveld method is a quantitative phase analysis method whereby weight or volume fractions of crystalline and amorphous phases can be determined.) Powder XRD also identified the crystalline phases present. (See “Ceramic Pigments and the European REACH Legislation: Black Fe2O3-Cr2O3, a Case Study,” by De La Torre, et. al., doi: 10:1111/j.1744-7402.2010.02528.x)

The group (out of Spain) studied three pigments, two black formulations and one brown composition. The black formulations were commercially available pigments comprised of Fe2O3 and Cr2O3. The brown composition was laboratory prepared and also was mostly Fe2O3 and Cr2O3, but with reduced chromia to accommodate additions of alumina, magnesia and traces of titania and silica, in order to study the effects of minor elements on the crystallography on the pigment. Using powder XRD, the black pigments were determined to be single phase, with a corundum structure and minimal amorphous content. The brown pigment was more complex, consisting of two phases with corundum structure, a magnesium chromate spinel phase and a small but measurable amorphous phase.

The researchers concluded that the Rietveld method is a valid approach to quantitative mineralogical analysis of pigments and an effective means for grouping pigments, and thus “narrow down the number of toxicity tests required to fulfill the REACH legislation.”

The paper does not explicitly mention QSARs, however, it does appear to demonstrate the necessary ability to classify materials into categories of substances and thereby reduce animal testing to one representative formulation.

According to the paper, grouping of substances could have a huge impact on the costs (monetary and biological) associated with animal testing. Initially, the EU estimated registration of 29,000 chemical substances requiring 2.6 million animals for toxicity testing. The authors note this is a gross underestimation and that over 100,000 synthetic chemical products are used worldwide, all of which will require toxicological assessment. Various scenarios generate estimates that range between 54 and 141 million animals required for REACH compliance alone, at a cost of at least €9.5 billion over the next ten years.


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