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Because of the relatively high tolerance allowed for clopyralid for public
safety, health, wildlife and environmental concerns, most laboratories do not
routinely measure either picloram or clopyralid below 50 ppb. Consequently,
potentially-injurious levels in straw, hay, compost, and other residuals are
often not detected. At WSU, an initial series of analytical tests of the compost
did not reveal any contamination from any suspected herbicides. However, after
consultation with a local commercial analytical laboratory, procedures were
modified and detection levels increased in sensitivity from about 50 to about 1
ppb.
Most herbicides break down rapidly after application. In two review articles on
pesticides in composting (Buyuksonmez et al. 1999; 2000), herbicides were
generally considered to break down during normal composting. However, some of
those in the pyridine carboxylic acid group such as clopyralid break down very
slowly, especially during composting. When ingested by animals, these compounds
pass through into the urine quickly and without significant degradation.
Regulations requiring “weed-free” straw for highway revegetation projects, 
for
local organic gardens, and for “weed free hay” on Federal lands may not take
into account the potential for contamination of herbicides used to create the
“weed free” product.
The label recommendations for clopyralid products state “Do not use compost
containing grass clippings in the growing season of application.” This label
recommendation was based on trials at Michigan State University (Vandervoort et
al., 1997). Although the research reported clopyralid concentrations decreased
during composting, after one year the reported concentrations ranged from 100 to
1,300 ppb of clopyralid in compost made from treated grass clippings. However,
these concentrations are 10 to 100 times the level known to cause injury in
sensitive plants. Thus, the label is probably not sufficient to protect
composting facilities because damaging levels may persist beyond the season of
application, as occurred in Spokane and at WSU.
THE SITUATION IN SPOKANE
The Spokane Regional Compost Facility at Colbert, owned by the city’s Spokane
Regional Solid Waste System, has been operating since 1993. Until recently, it
operated an open windrow site, processing 25,000 tons/year. The clopyralid
problem first surfaced in 2000 when injury was noted on tomatoes grown in
containers with compost from the Colbert facility. The contamination persisted
and was traced to lawn clippings brought to transfer stations and later to the
Colbert facility for composting. After investigation by the Washington
Department of Agriculture, the sale of the compost was halted. The facility now
has 25,000 cubic yards (cy) of unsold compost.
Samples of this material taken in January, 2001 (nine months after the problem
was discovered) still showed clopyralid residues of 31 to 75 ppb. A limited
amount of the compost from the 1999-2000 season has been sold to landscapers and
other wholesalers but with the understanding that it could be used only on turf,
not gardens (sales always have been wholesale — the facility’s permit 
doesn’t
allow retail sales). Purchasers had to sign a waiver and name the city on their
insurance policy. The Spokane Regional Solid Waste System has received only a
few claims for damage from the compost, and they have been settled.
In fall of 2000, Norcal of Spokane took over operation of the Colbert facility
and is presently producing compost using an Ag-Bag aerated windrow system
(previously turned windrows). It was hoped that a change in the composting
method would lead to better degradation of the herbicide. However, traces of
clopyralid still persist, preventing the sale of the compost to the public. This
compost was produced in fall 2000 from feedstocks consisting of leaves, traces
of grass clippings, and other yard trimmings. Norcal sampled the bagged material
in March 2001 and clopyralid was present at 57 to 67 ppb. In May 2001, the
finished compost from these bags failed a bioassay test. Contamination levels in
this material have now been tested at 73 and 80 ppb.
In April 2001, the city and Spokane county asked Dow to voluntarily halt
distribution of clopyralid in the Spokane area, at least temporarily, and they
have agreed to do so for residential uses. Application will still continue at
golf courses where grass cycling is practiced. Grass from golf courses and parks
is not taken to the composting facility. Dow has prepared a flyer for landscape
companies asking their cooperation and suggesting alternatives they can use.
Norcal continues to accept all yard trimmings material, including grass. A
screening process for raw feedstocks is being considered but has not been
implemented. However, the city has increased its public education campaign,
distributing information telling people why herbicide-treated grass cannot be
composted.
Norcal is working with Dow on a research project seeking a way to break down
clopyralid in compost. The Scope of Work includes testing residues in grass from
test plots at different intervals after spraying, as well as composting in a
laboratory setting under a variety of conditions.
THE SITUATION AT WSU
In Pullman, Washington, 80 miles south of Spokane, WSU produces 25,000 cy of
compost from animal manure and bedding, collected from the university farms and
research facilities. The product is sold to nurseries in eastern Washington and
northern Idaho as straight compost and is also blended by nurseries in a 50-50
compost/soil mix.
WSU first faced the herbicide issue in 2000 when picloram, a compound closely
related to clopyralid, was detected in its composts. The source of contamination
was eventually traced to a pasture sprayed with Tordon-101, a product containing
picloram and 2,4-D — both herbicides used to control broadleaf weeds. This
pasture was later harvested for hay (off label), which was fed to livestock. The
manure and bedding taken to the WSU composting facility carried the picloram
with it. Compost was sold to nurseries and later to homeowners who discovered
plant-deforming symptoms on peas, beans, tomatoes, potatoes, sunflower and
certain shrubs. The incident put WSU on the alert, and they instituted a regular
testing program for herbicides, including both analytical tests and bioassay
with plants.
While the picloram contamination resulted from an isolated incident, in the
spring of 2001, compost from WSU’s windrow system was found to contain
clopyralid in concentrations from traces to over 200 ppb. The source of
contamination is believed to be from grass hay and straw used in their animal
feeding operations. During 2000 and 2001, WSU performed extensive testing on hay
fed to livestock and straw for bedding to identify sources of contamination. Now
WSU is certifying vendors of grass hay and straw. Dan Caldwell, farm and compost
manager at WSU, has told vendors that they have to be certified by WSU to sell
grass hay and straw. To be certified, vendors will have to guarantee that their
product is free from herbicide contamination. “Some may decide not to
participate. Others will become certified vendors, and they are the only ones we
will purchase from,” Caldwell says.
Since the original incident, WSU has since taken a proactive position, advising
homeowners on the contamination and offering advice and compensation to affected
compost users. WSU initiated community meetings with the public and began a
bioassay test program for soils suspected of being contaminated from the
compost. A bioassay involves growing sensitive plants for a few days and
watching for signs of stress. WSU used tomatoes, beans, and peas as indicator
plants. Analytical tests were conducted to confirm the presence of picloram and
clopyralid. Remediation strategies such as frequent watering and cover crops
were recommended to facilitate breakdown of the chemicals.
This spring, WSU has tested garden soil from the public for possible herbicide
carryover from last year’s application. When needed, WSU has provided 
activated
charcoal to homeowners as a means of reducing or eliminating the damage and
allowing gardeners to plant their gardens this year. In some cases, where the
recommended amounts of compost were applied (one inch in depth or less), the
soils were sufficiently free of the herbicide to grow a garden. Where higher
amounts of compost were applied in 2000, sensitive plants were still affected in
2001. WSU has not sold any compost for the past two years.

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heidi larson




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