Methodology

Background on XRF Testing, Detailed Methodology and Methodological Limitations

HealthyStuff.org product tests are performed with a portable X-ray Fluorescence (XRF) analyzer. XRFs are widely used by both product manufacturers and government regulators to screen consumer products for hazardous chemicals. XRFs, like all test methods, have limitations. Researchers selected products based on our research interests and consumer interest. The sampling was not random or necessarily designed to be representative of all products on the market. This page provides an overview of the product testing methodology used by HealthyStuff.org, including:

XRF Testing Methodology

Researchers tested products using a High Definition X-Ray Fluorescence (HDXRF) manufactured by X-Ray Optical Systems (download XRF Factsheet). The HDXRF analyzer uses a technology known as x-ray fluorescence spectrometry to detect chemical elements, such as lead, cadmium, chlorine, arsenic, mercury, tin, and antimony. The major benefit of HDXRF is that monochromatic excitation eliminates the X-ray scattering background under the fluorescence peaks, greatly enhancing detection performance. This analytical approach results in detection limits in the parts-per- billion (ppb) range for many elements of interest in a variety of materials.

Typical HDXRF element detection levels

The elemental composition of the materials reveals the presence of potentially hazardous chemicals, such as metals, and also allows researchers to infer the possible presence of toxic chemicals or materials, including brominated flame retardants (BFRs), polyvinyl chloride (PVC) and possibly phthalate plasticizers. We have translated the research results into a HealthyStuff.org product rating system to allow users to easily compare the chemical levels of a variety of consumer products. There are a number of chemicals of concern that cannot be detected by this technology.

X-ray Flourescence (XRF) Background Material


Quality Assurance/Product Variation - In order to evaluate the variation per product to assess and verify the accuracy of our testing, some repeat samples were taken. This process took place once every 200 samples, and was done for at least one product in every product category. Repeat samples are taken in three different ways:

  1. three readings taken from the same sampling location of one product
  2. three readings taken from three different sampling locations (consisting of the same material, color, etc.) on the same product
  3. three readings taken from the same sampling location on three different but identical products

All repeat sample data was recorded and submitted for review, but is NOT included in the product database.

Data Interpretation - We interpreted the results using the concentrations and deviations reported by the analyzer, together with visual examination of the spectra generated by the instrument. The analyzer reports concentrations of elements by analyzing the spectra using reference data for the elements it reports, and measuring the area under the curve in the spectrum. We visually examined the spectra to confirm the presence of elements with known interferences (lead, bromine, and arsenic), and have not reported them where we could not confirm presence.

Methodological Limitations

The levels of lead, cadmium, chlorine, and other elements shown in this website are those reported by the HDXRF analyzer manufactured by X-Ray Operating Systems. Our testing methodology uses standards with known levels of certain elements to check the accuracy of the analyzer in one type of matrix material. However, the products we tested are made of many different types of materials, in some cases even within the same product. The prescence of materials may interfere with the analyzer's ability to quantify the elements accurately. When the materials in a single product are not homogeneous, the test results may vary depending on the orientation between the object under test and the testing device. Where the testing is not able to isolate a single material, the reported levels may represent an averaging of the levels in the different materials. Interferences can occur between elements as well, such as with lead and arsenic, resulting in poorer precision. Test results are reviewed for possible inference.

Therefore, the levels we report provide a general indication of the levels in the products in order to guide consumers on product choices. More exhaustive testing with XRF, as well as laboratory testing, could provide more detailed findings on the levels of elements and associated compounds.

HealthyStuff.org ratings do not provide a measure of health risk or chemical exposure associated with any individual product, or any individual element or related chemical. HealthyStuff.org ratings provide only a relative measure of high, medium, and low levels of concern for several hazardous chemicals or chemical elements in an individual product in comparison to criteria established in the site methodology.

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