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 handheld X-ray fluorescence (XRF) device manufactured by Innov-X Systems (download XRF Factsheet). The XRF 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 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.

As several different organizations contributed data to this project, researchers conducted tests in several locations across the country. The exact XRF device sampling protocol is described below.

XRF Calibration - XRF machines were calibrated at the beginning of each round of sampling using the stainless steel clip, as well as the EC681 standard. Both calibrations were done once with a test length of 60 seconds. Results were compared to the known levels in the sample. During testing, a standardization was taken after every 200 readings, using both the stainless steel clip and the EC681 standard. In addition, one time standardization was performed with Wako Chemical USA ABS discs with cadmium, chromium, lead in high & low concentrations (NMIJ CRM 8106-a & NMIJ CRM 8105-a) and PVC disk standards (low and high concentrations). This can lead to an averaging of the chemicals of concern when near-surface materials are non-homogenous. This may lead to an underestimation of the level of chemicals of concern in a product.

Testing - Standard testing time was 30 seconds. The XRF machine was preset to test for the full 30 seconds. Only one test was taken per component/material of a product. An attempt was made to sample major components/materials of each product. The actual number of samples per product varied. Because the X-ray penetrates from just a few microns (metal) to 1/4 inch (plastics and other softer substrates), the measurement should be considered a surface or near surface measurement.

Background sampling - Prior to the start of testing, the background material was sampled with the XRF. The same background was used for all samples, whenever possible. When backgrounds were used, they were free of all chemicals of concern.

Machine positioning - When sampling, the XRF machine was held in a position perpendicular to the product being tested, without compressing the material. Tests were conducted on the flattest part of the product, and the entire analyzer window was covered by the material being tested, when possible. Products were not dismantled to test interiors.

X-ray Flourescence (XRF) Backgound Material


Levels of Detection - LODs for highlighted elements are as follows:

 

Element Manufacturers
Detection Limits(1)
Observed Detection Limits
(30 second sample)(2)
Antimony 50-150 ppm 109 ppm
Arsenic 10-100 ppm 1 ppm
Bromine 10-100 ppm 2 ppm
Chlorine 1% - 5% 2.80%
Chromium 10-100 ppm 39 ppm
Cobalt 10-100 ppm 37 ppm
Copper 10-100 ppm 38 ppm
Lead 10-100 ppm 5 ppm
Mercury 10-100 ppm 7 ppm
Nickel 10-100 ppm 27 ppm
Tin 50-150 ppm 130 ppm

(1) InnovX Model ABC XRF Detector detection estimates based on 1-2 minute test times and detection confidence of 3-sigma, or 99.7% confidence. Detection limits are a function of testing time, sample matrix and presence of interfering elements.
(2) Observed detection limits varied by type of material being tested. Detection limits presented here are the lowest observed from all testing.

 

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 XRF analyzer manufactured by Innov-X Systems, Inc. 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 the 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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