USEPA/OPP - U.S. Composting Council Meeting--Persistent Herbicides in Compost, July 16, 2015

USEPA/Office of Pesticide Programs (OPP) Attendees:

Pesticide Re-evaluation Division: Tracy Perry, Veronica Dutch, Kelly Sherman

Registration Division: Kay Montague, Reuben Baris

Ecological Fate and Effects Division: William Eckel

Health Effects Division: Christina Swartz, Doug Dotson

U.S. Composting Council (USCC) Attendees & Partners:

Cary Oshins - USCC

Craig Coker, PE, Coker Composting & Consulting

Dr. Fred Michel, Ohio State University

Meeting Summary

• The USCC requested an update on the registration review status of certain herbicides (i.e., 

aminopyralid, clopyralid, picloram) that may persist through the composting process and cause 

damage to non-target plants receiving the composted material. OPP explained that it is preparing to 

formally require, through the Agency’s Data Call-In process, the data needs that are outlined in the 

final work plan for these pesticides. Several special studies will be required that are expected to 

inform the Agency’s understanding of how persistent these herbicides are in compost and manure

(i.e., dissipation in compost and associated environmental chemistry methods). OPP requested 

USCC assistance in identifying representative composts to be used in the special studies. 

• The USCC also emphasized their interest in access to inexpensive methods to detect the presence of 

persistent herbicides in feedstocks received for composting.

• OPP noted that new herbicides of similar chemistry to these three pyridine herbicides are being 

screened for potential compost issues before their registrations are granted and that the risk 

assessments for these new herbicides would be available in the public docket.

• Given the movement to ban disposal of food wastes in landfills and redirect them to composting 

facilities, the USCC expressed concern regarding potential residues of persistent herbicides in food 

waste. OPP noted that actual levels of pesticides in/on foods are often orders of magnitude lower 

than tolerances, which are the maximum legal levels for enforcement purposes. Residues of 

persistent herbicides in food waste are not expected to be a significant source of exposure in 

compost. 

• Dr. Michel presented his recent national survey of commercial composting facilities, in which three 

out of 70 composts tested exhibited herbicide phytotoxicity symptoms. There was no correlation of 

phytotoxicity with location, feedstock, or composting method. 

• USCC has set up a confidential incident reporting system for composting facilities and has received 

three phytotoxicity reports this year.

• OPP noted that the meeting summary and a copy of Dr. Michel’s presentation would be added to the 

registration review dockets for picloram (EPA-HQ-OPP-2013-0740), aminopyralid (EPA-HQ-OPP2013-0749), and clopyralid (EPA-HQ-OPP-2014-0167).
How Widespread are Persistent Herb

Results of a Nationwide Compost S

Frederick C. Michel Jr.*, Katherine M. Speicher, Bing Zang, Luis 

Department of Food, Agricultural and Biological Engineering

The Ohio State University, 1680 Madison Avenue, Wooster, OH USA 4

*michel.36@osu.edu
Persistent Herbicides

 Clopyralid, Aminopyralid, Aminocyclopyrachlor, Piclo

 Active ingredients in over 30 herbicides

 Highly effective at low dosages with very low human, 

and aquatic environment risk.

 Control annual and perennial weeds in crop producti

as well as invasive weeds in natural areas and pasture

 Effective against Creeping Thistle, Creeping Charlie an

noxious, and invasive difficult to control perennial br

weeds.

 Persistence and potency means fewer applications.

 Feed stocks such as turf, manure, food waste, dead tr

hay may can contain residual amounts of these herbi
Aminocyc

6‐amino‐

Cycloprop

4‐carbo

Clopyralid

3,6‐dichloro

2‐Pyridine carboxylic acid

Aminopyralid

3,6‐ dichloro ‐

2‐Pyridine carboxylic acid

1‐amino

N

Pyridine/Pyrimidine Carboxylic Acid Herb

4‐Amino‐3,5,6‐trichloro‐

2‐Pyridine carboxylic acid

Picloram
Pyrimidine/Pyridine Carboxylic Acid Herb

Active Ingredient

Name Manufacturer

First

Registered Trade Names

Obs

Lev

Picloram

DowAgroSciences

1963 Tordon, Grazon, Access,

Pathway

Clopyralid

DowAgroSciences

1978

Curtail, Redeem R&P,

Transline, Confront,

Lontrel

Aminopyralid

DowAgroSciences

2005 Milestone, Forefront,

Chaparral

Aminocyclopyrachlor DuPont 2010 Imprelis, Perspective,

Viewpoint, Streamline

Soil testing labs cannot reliably measure the concentrations

of these chemicals in composts at levels below 10 ppb
Aminopyralid in YT Compost (ppb d

0 10 50 10

Concentration value

are the overallconcentrations in thmedia.
Dairy Manure Compost Control

50% Compost

No detectable Herbicides in Compost
52 week old compost

50% Compost

Herbicides detected = 6 ppb aminopyralid, 7 ppb 
Allowable herbicide concentrations in fo
Treatments (Values are mg/kg) 

Sample day 

Untreated Granular Herbicide Liquid Herbicide 

wet wet dry ash wet dry ash wet 

Day 0 NT 1.5±0.3 5.2±1.0 37.5 ±8.1 3.8±0.4 13.4±1.2 85.2 ±15.1 34±4 Day 1 0 NT 2.0±0.4 6.9±1.5 37.8 ±7.7 4.7±0.9 17.1±2.5 82.9 ±19.0 44±5 Day 30 NT 2.9±0.5 6.9±1.6 34.6 ±8.0 6.5±1.4 16.7±2.2 73.8 ±17.8 47±1 Day 50 NT 3.0±0.5 6.5±1.6 31.2 ±7.8 6.7±1.4 17.2±2.9 69.7 ±18.5 53±4 Day 78 <0.01 3.5±0.5 6.3±1.5 28.9 ±6.2 6.6±1.6 16.1±2.0 62.8 ±14.3 49±4 Day 100 <0.01 2.8±0.5 6.5±1.6 28.7 ±7.5 6.6±1.2 15.3±2.1 59.4 ±13.8 50±4 Day 178 NT 2.5±0.7 4.8±1.6 20.0 ±6.2 6.9±1.2 10.7±2.2 37.0 ±12.1 31±2 

Difference % Loss +67% -8% -47% +82% -20% -57% -9% 

Concentrations of PH Herbicides during Composting

Compost

Age
Concentrations of Persistent herbicides in Comp

of different ages at an impacted facility

Weeks
• Compost samples (2 kg) requested from all USCC me

– Compost was to be, “just ready for sale or use”.

• Facility information also requested

– Location– Compost age

– Feed stock(s) used

– Composting system(s) employed

• Windrow, Aerated Static Pile, In vessel, etc.

– Whether there have been complaints about compost dam

Survey of US Composting Facilit
Sources of survey compost
Feedstocks

31%

38%
Ages of survey composts

Mean = 8.1 ± 8.2 months

Compost

Age

(months)

51% are 6 
Herbicide Bioassay

• Plant growth media

– 50% Compost

– 50% Peat based potting mix

• Moisture adjusted to 80% saturation• Sown with four garden bean seeds, culled to one

– Very sensitive to pyridine and pyrimidine carboxylic acid 

• Incubated in greenhouse at > 60 F

• Artificial lighting in Winter, 12h per day

• Plants watered daily to original weight

– Deionized or distilled water used

– No drainage to prevent herbicide wash out

• Plant health assessed after 35‐50 days

– Leaf shape, Leaf number, height, dry weight
Results of Phytotoxicity Testi

• 70 composts tested

– 4 showed leaf curling

• New England, Midwest, Southeast, Northwest

– 3 exhibited loss of apical dominance

• New England, Midwest, Southeast

– 3 sites reported herbicide problems

• New England, Midwest, Northwest

– 13 sites received horse manure/bedding f
Leaf curling

and

malformation

(Positive control)

L

of 

Dom

(teste

No symptoms

(tested sample)
Herbicide Concentrations in

Test Composts and Controls

Sample

EC

Amino

pyralid

Picloram Clopyr

alid

Loss of

Apical

Dom.

Leaf

Curling

(DS/m) (ppb) (ppb) (ppb) (Y/N) (Y/N)

Compost A 1.65 0.1 3.3 2.2 N N 

Compost B 7.27 2.3 3.6 6.6 Y/Y Y/Y 

Compost C 1.28 1.7 18.1 2.4 Y Y 

Compost D

+ 1 ppb AP

1.80 9.28 6.5 3.3 N* N* 

Compost O

Negative

control

‐ 0 0.5 0.9 N N 

Compost M

Positive

Control

1.73 0.6 2.1 0.3 Y/N Y/N 
• Chemical testing to determine the concentrations of herbicides 

samples.

• Reliable plant bioassays to screen composts and feed stocks for 

contamination.

• Development, validation and publication of chemical test meth

measurement of herbicides in composts at ppb.

• Determination of the fate and persistence of recalcitrant herbic

composting and in soil.

• Research on low cost methods to remediate contaminated com

– Inoculants that are enriched with microorganisms able to degrade recalcitr

– Adsorbents for herbicides in composts

Research Needs
Questions?
Growth Variation in Compo

• Under the same growth

conditions plant growth response

differed in different composts

• Plants grown during different

seasons also had different

responses
Herbicide Phytotoxicity Symptoms
Remediation of Herbicide Toxici

• Five additives tested

– Activated Carbon, Zeolite, Wood Ash, Biochar, 

• Added to 2% on a dry weight basis

• Compost added at 20%

• Aminopyralid added at 0, 3, 32, 128 and 6

• Plant growth assessed

– Leaf curling, germination, loss of apical domina
Activated Carbon (2%)

Aminopyralid Concentration (ppb = ng/g compost dw)

639 ppb 128 ppb 32 ppb 3 ppb 0 

No

Germination
Osorb (2%)

Aminopyralid Concentration (ppb = ng/g compost dw)

639 ppb 128 ppb 32 ppb 3 ppb 0 ppb
Zeolite (2%)

Aminopyralid Concentration (ppb = ng/g compost dw)

639 ppb 128 ppb 32 ppb 3 ppb 0 ppb
Wood Ash (2%)

Aminopyralid Concentration (ppb = ng/g compost dw)

639 ppb 128 ppb 32 ppb 3 ppb 0 ppb
Phytoxicity Scale (0‐4)

DeadLADNone

ppb Aminopyralid
Conclusions

• Properties of compost from around the US vary

– EC 1 to 11 dS/m, pH 5.6 to 8.8

• Plant growth response in compost media was also v

– Time, season, temperature

• 3 of 70 composts exhibited herbicide phytotoxicity• No correlation with location, feedstock or method

• Wood ash and activated carbon at 2% remediated

contaminated composts with 30 to 600 ppb aminop