Accuracy and Precision of Analyses for 2,4-D and Picloram in Streamwater by Ten Contract Laboratories

Abstract

In a test of laboratory precision and accuracy, streamwater samples fortified with 0, 10, or 50 μg ae/L 2,4-D [(2,4-dichlorophenoxy)acetic acid] and picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) were submitted in quadruplicate for residue analysis to 10 laboratories that analyze samples for a fee. Varying amounts of the herbicides were detected by eight laboratories, and two reported no residues. Analyses from most laboratories had a negative bias (ranging from −2 to −92%), although a positive bias appeared in a few instances. Precision was highly variable, the coefficient of variation ranging from 3.4 to 200%. The accuracy range in 19 of 20 cases was ±100 to ±78% for 10 and 50 μg/L 2,4-D and ±100 to ±114% for 10 and 50 μg/L picloram, respectively. Results show that careful selection of contract laboratories and a quality assurance program should be part of monitoring for water contamination with herbicides.