GLP Herbicide Bioassay

PIRM Bioassay for herbicide injury of 5 different composts, followed by a rank-order statistical damage code.
Woods End’s short-term plant-response bioassay has been carefully developed over decades and can detect trace levels of plant-active auxinic herbicides in soil and compost that may be relevant to practical plant culture. The test uses a variety of specially selected cultivars varying in sensitivity against suitable controls to detect very low amounts of bioactive auxinic herbicides capable of impacting plants. Chemicals belonging in the class of auxins may include 2,4-D, Dicamba, Clopyralid, Picloram and Aminopyralid and range in bioactivity thesholds from 1 ppb to as high as 0.5 ppm.

Test Procedure is based on a GLP process documenting each step of the process. Seeds may be germinated in a Standard Soil (CEN control soil) or equivalent Standard Grow-Media to which is added specific volumes of test material (compost or soil with suspected contaminant). After a suitable growth interval under controlled conditions, the plants are statistically ranked on a bioassay scale using appropriate bio-indicators determined from previous calibration assays. Results are keyed into a computer program that interpolates injury-index potential (PIRM).

REGULATORY INFRASTRUCTURE: Residues of pesticides used in lawn, garden and farm occur frequently in organic residues but may not pose any risk depending on molecular composition. Characterizing the decay kinetics (“fate”) and potential phyto-toxicity (“Effect”) is important for proper product registration and consumer protection. The occasion that these residues become troublesome when recycling via composting or soil application may be rare but must always be characterized. Woods End is the world’s leading lab to fully characterize the decay potential ade downstream risk potential.

HERBICIDES FOCUS: A wide category of herbicides are used in agriculture and horticulture. The types most likely to influence plants when organic matter is recycled are those known to have carryover potential in crop rotations. Farmers have mostly learned how to manage post-application damage by choosing which crops follow in a rotation. However, this context is challenged by composting and product labels need to be updated to include this as a “fate pathway”. An example would be applying composted animal manure to grass-legume fields causing a shift to monocot prevalence.

VEGETABLES AFFECTED: Consumer impact is also evident. Certain common vegetables are variously sensitive to herbicide carryover outside label guidelines, posing a unique challenge for manufacturers and applicators. Auxins for example are not labeled for tomatoes and there is no tolerance limit. However, auxins present in compost will affect tomato growth sometimes leading to epinasty.

LAB ANALYSIS: Laboratory testing using “GC-MS” (Gas Chromatography/Mass Spectrometry) is always warranted to pinpoint molecules present, but cannot determine bioactivity-injury potential. Thus GC-MS alone may be very misleading in imply a danger when none or little exists for actual growing plants.

PLANTS AS BIOASSAY: Woods End has worked carefully over two decades to develop effective plant herbicide detection methods that are relevant to what a grower will experience. The bioassay technique distinguishes plant sensitivity groups. The test predicts the probable level of bioactive herbicide calibrated to a known molecule.

Plant Injury Risk Management: The final result of Woods End herbicide bioassay test is “PIRM” – Plant Injury Risk Management. With this tool the likelihood of passing on risk to customers is largely obviated.

Contact us: if you have concerns about chemical compost residues: we’ll help you manage it.