Envirologix: Putting Science to the Test

USDA GIPSA Guide: Sampling for the Detection of Biotech Grains - Part 1

October 2000

Reproduced by permission of USDA GIPSA

Introduction

A consignment of grain (or grain lot) has many unknown quality characteristics. Measuring these characteristics on the entire lot can be costly. An experienced inspector must examine the grain to determine whether a kernel is damaged or not. Time constraints and cost prohibit an inspector from examining every kernel in a grain lot. Inspecting a small subset of the lot is much less costly and time consuming than inspecting the whole lot. This subset of the lot is called a sample. GIPSA has instructions for taking samples from static lots - such as trucks, barges, and railcars - and for taking samples from grain streams. Grain Inspection Handbook, Book 1, Grain Sampling contains these instructions and can be obtained by contacting GIPSA, ordering through the GIPSA Publications Web site or by viewing/printing from the GIPSA Handbook site (Requires Adobe Acrobat Reader; this is a 63 page document and may take a minute or so to load) .

While inspecting a sample is much less costly than inspecting the entire lot, the content of a sample does not always reflect the content of the lot. Fortunately, when samples are properly taken, probability theory can assign some risk values to measurements on samples.

Furthermore, sampling from a lot is only one source of error when estimating a quality characteristic of a lot. Sources of error fall into three basic categories: (1) sampling, (2) sample preparation, and (3) analytical method. Sampling is an ever-present source of error when estimating characteristics of a lot. However, depending on the characteristic being measured, sample preparation and analytical method can be significant contributors to measurement errors. Minimizing these errors is necessary to assure better precision and accuracy in the final analytical result.

Buyers and sellers of a lot have to agree on the quality and price of the lot before a transaction can take place. Basing the quality of a lot on a sample introduces risk to both buyer and seller. Buyers and sellers want to control their risk where possible. Using the information provided in this paper, buyers and sellers will be able to make informed decisions.

This paper discusses sampling errors associated with detecting the presence of biotech varieties in grain lots, and presents ways to estimate these errors and control the risks to buyer and seller. The paper does not recommend any specific sampling plan. Buyer and seller should agree on a sampling and testing plan that best meets their mutual needs.

Next...

PDF files, where provided, require Adobe Acrobat Reader.

- up -