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More on the Methods

Jun 27, 2019

There has been some confusion about the methods of the Emory Study showing that organic tests clean for antibiotics and pesticides, and has 20 times lower levels of growth hormones than conventional milk. There have also been some erroneous criticisms of the methodology, which are rooted in a lack of knowledge about testing for toxicants.  Here are some additional details about the methods, addressing some questions that have been brought up:

The researchers used a median average instead of the mean because the distribution curve found in the study was non-normal. This is a well-known (and well-used) tool for providing an average for samples without a normal distribution curve.

Also, the methods used in this study are more sensitive than the rapid test strips used in the field. The FDA limits of detection, below which the field tests can’t detect the presence of antibiotics, were set back in the 1980’s before we had more accurate testing methods, and are designed to give a quick yes or no as to the presence of specific antibiotics rather than an accurate reading of the antibiotic levels.  These methods are not negating or opposing the past FDA study findings, they just look more carefully at what is in retail milk, and can look at lower levels than past FDA studies.  Also, the lab tests were done blind, with the people in the laboratory unaware of which samples were organic or conventional, to avoid any potential bias.

When it comes to the high-performance liquid chromatography (HPLC) methods used by the study, the researchers coupled these to tandem mass spectrometry or high resolution mass spectrometry rather than just using HPLC alone, which is an important distinction. Methods using these techniques are considered the most selective and sensitive allowing you to filter out chemical “noise” in the samples that may be present such as fats and proteins.  For example, this type of instrumentation is used to confirm dipstick drug tests for drugs of abuse or doping in sports because these techniques are the most scientifically defensible.

While uncertainty increased as levels approach the limit of detection, this is true of any analytical system including dipstick measurements using the inhibition test used on milk. For statistical evaluations, it is typical to assign a value of 1/2 the LOD or LOD divided by the square root of 2 to determine means, medians and percentiles or even to perform t-tests. These are methods customarily used by scientists evaluating data because you assume there is some distribution of actual levels below the LOD.

The methods for this study were developed by the leading expert on environmental toxicant detection, Dr. Dana Barr of Emory University. Dr. Barr has authored over 300 peer-reviewed publications, and prior to her academic tenure she worked with the Center for Disease Control for 23 years, where she developed methods for assessing human exposure to a variety of environmental toxicants.  She has also received numerous awards for her research (eg. ISES’s Daisey Award for Outstanding Investigator, two HHS Secretary’s awards, 2004 Federal Scientific Employee of the Year, CDC’s Mackel Award, and EPA’s Silver Medal).  She is a three-time recipient of the Thomson Reuters “Most Highly Cited Researcher” award representing the top 1% of researchers in ecology and the environment over the previous 10 years.  She is the foremost expert in the field, and her work has been the basis for many currently used methods that have advanced our ability to understand human exposure to chemicals.

These methods are more sophisticated and advanced than the older FDA-approved methods.  Chemical testing methods have advanced dramatically in the last 30 years – we should use those advancements to better understand what toxicants we are exposed to.

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