Healthy soil and sustainable growing

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More details on what happens to toxins in compost...


Questioning the compost supply chain

As politicians increasingly use composting to 
solve municipal waste and recycling issues, what 
happens to the pesticides, herbicides and 
pharmaceuticals that may have gone into the mix 
along with the lettuce leaves


Deborah K. Rich, Special to The Chronicle

Saturday, May 5, 2007

<http://www.sfgate.com/cgi-bin/object/article?f=/c/a/2007/05/05/HOGD3PJOUT1.DTL&o=0&type=printable> 


If soil, which breaks down fallen plant and 
animal materials, can be likened to the Earth's 
liver, then composting is becoming the liver of 
modern society -- tasked with processing and 
reducing lawn clippings, food scraps, manure and 
sewage. Given the chemicals we spray on our 
lawns, feed our livestock and swallow to keep us 
happy and functioning, are we asking too much of 
our collective microbial liver? Can composting 
detoxify chemicals, or are we spreading heavy 
metals, pesticides and drug residues in our 
gardens?

The answers to these questions are uncertain.

Composting is the mixing and management of 
organic waste (plant and animal materials and 
byproducts) to achieve ratios of carbon to 
nitrogen that accelerate and maximize microbial 
degradation of organic matter. By harnessing the 
power of microbes, municipalities can reduce and 
recycle plant and animal waste even where land 
and time are too scarce to accommodate the soil's 
comparatively slow rate of decomposition. "By 
composting, you are duplicating what nature would 
do given the chance," says Dale Arnold, director 
of quality control and research at Kellogg Garden 
Products. Kellogg sells compost and other soil 
amendments to 3,500 independent retail nurseries, 
as well as Home Depot and Lowe's. "Nature takes a 
long, long time to make compost. All we're doing 
is speeding up that natural cycle."

Yard trimmings, wood waste from construction, 
animal manure, agricultural byproducts and 
biosolids from sewage treatment plants are the 
primary feedstock for the roughly 170 composters 
and waste processors that operate in California.

All are valuable sources of carbon and plant 
nutrients, and these materials, once composted, 
can be used to maintain and improve soil health 
and productivity. Adding composted organic 
materials to soil improves soil fertility and 
structure, thereby lessening dependence on 
synthetic nitrogen and counterbalancing the heavy 
drawdown of nutrients and the successive 
degradation of soils that result from continuous 
farming and gardening. Soils high in organic 
matter are more porous, more drought resistant 
and less prone to erosion than are soils lacking 
organic matter.

Chemicals remain

Often these feedstock materials enter the 
composting process still laden with chemicals. 
Yet standards for finished compost, which vary 
from state to state, generally require regular 
testing only for heavy metals and pathogen 
indicators. Seldom do states ask that producers 
test their compost for residual pesticide or 
pharmaceutical compounds.

Unlike farmers composting manure and plant 
residues for their own use, gardeners purchasing 
compost at a nursery seldom know what went into 
the compost, where the feedstock came from or 
what chemicals were on them.

"Compost," says William Brinton, founder and 
president of Woods End Laboratories in Maine and 
a pioneer of modern compost production and 
testing systems in the United States, "has become 
anonymous and untraceable; a single compost 
product can now contain a mixture of unknown 
ingredients from all over a county or a state."

The compost supply chain is poised to become even 
more difficult to trace as city and state 
politicians turn to composting as a means to meet 
their solid-waste reduction goals. "Composting 
now is being driven by recycling mandates set by 
politicians," Brinton says. "When I got my start 
in the composting world in the '70s, our 
motivation was to create products that nourished 
the soil. That was the goal, and then we worked 
backwards and asked how do we take ingredients 
like manure and crop residues and make wonderful 
compost for the soil?

"Now it's the cart pulling the horse: The 
recycling cart is pulling the compost horse. I'm 
not saying the goals of making good soil 
amendments and recycling are incompatible. I'm 
saying that this sets up the challenge to 
maintain the integrity of compost, a challenge 
that will become more intense as the industry 
grows even larger."

Aside from the standards set by the National 
Organic Program for compost used in organic food 
production systems, national standards exist only 
for composts made from solids captured in the 
treatment of sewage at municipal wastewater 
treatment facilities. In 1993, the EPA developed 
heavy metals and pathogen standards that sewage 
solids -- also known as sewage sludge or 
biosolids -- must meet before they can be spread 
on land. Subsequently, these same standards were 
extended to compost made from biosolids and sold 
to wholesalers and retailers.

The California Integrated Waste Management Board 
regulates composting in the state and requires 
that all compost produced in California meet the 
heavy metal and pathogen indicator standards set 
by the EPA for biosolids, regardless of feedstock 
source. California does not require testing for 
chemical residues such as pesticides, antibiotics 
or hormones.

Heavy metals, many of which -- like lead, arsenic 
and cadmium -- are toxic to humans at low levels, 
aren't subject to microbial degradation in soil 
or compost systems. Preventing their buildup in 
soil requires restricting how much is added to 
the soil in biosolids, compost or any other soil 
treatment.

Some scientists are concerned whether heavy 
metals standards developed for land application 
of biosolids are appropriate for compost because 
compost is often applied at much higher rates 
than those allowed for sewage sludge.

"I think it is a very different story when you 
are applying compost heavily over a short term 
than when you are applying smaller amounts of 
sewage sludge over the long term because the 
bioavailability of these compounds is very 
different when they're freshly applied and fresh 
material," says Tom Richard of the department of 
agricultural and biological engineering at 
Pennsylvania State University. "There is a lot of 
organic-matter cycling going on, and these 
minerals will go through more available phases as 
they cycle round."

To qualify for unrestricted use on organic farms, 
compost must have lead, cadmium and arsenic 
levels two to four times below those permitted by 
EPA standards for the highest-quality biosolids.

Drugs break down

Unlike heavy metals, human and animal drugs have 
been repeatedly shown to break down in both soil 
and compost. "In general, drugs, once they hit 
manure, are metabolized relatively quickly," says 
Michael Payne, dairy program coordinator for the 
Western Institute of Food Safety and Security. 
"When you add a proper compost step, you even 
accelerate that because of the heat."

A recent study of composting examined its ability 
to break down 10 pharmaceutical and personal-care 
product residues in biosolids collected from a 
wastewater treatment plant in San Diego. Fatih 
Büyüksönmez, of San Diego State University's 
department of civil and environmental 
engineering, found that composting for 45 days 
reduced residues of 9 out of 10 products by at 
least 85 percent.

Hormone residue in sewage and animal waste 
appears to be similarly reduced by the composting 
process; they are natural compounds and highly 
susceptible to microbial degradation. But how low 
a level of hormone residue is safe is unclear. 
Scientists are finding that even very low levels 
of hormones -- washed into streams in municipal 
and dairy wastewater -- can significantly affect 
fish and amphibians. Research is also linking 
hormones to increases in a variety of human 
diseases, including some cancers.

A study published in 2005 by Heldur Hakk of the 
USDA's Agricultural Research Service found that 
composting reduced the incidence of estrogen 
(17B-estradiol) and testosterone in chicken 
manure by 84 to 90 percent in 139 days.

In his discussion of results, Hakk cautions that 
the rate of hormone degradation will be affected 
by how well the compost is aerated, and by the 
moisture level, porosity and particle size of the 
compost.

Time makes a big difference

Time, says Brinton of Woods End Laboratories, is 
another key variable in the reduction of hormones 
through composting, and of antibiotics and other 
drugs as well.

"If you use very short turnaround systems, the 
breakdown of these drugs is a concern,'' Brinton 
says. "Most composters are composting 60 days at 
least, and some composters are waiting six to 
eight months because they know the compost only 
gets better and better. Every once in a while I 
hear of a five-day compost system, and that's 
just not long enough. Most states say you can 
meet EPA law in five days with in-vessel 
composting, or 15 days for other systems, but 
then you need to store it for 30 days. So some 
safeguard is built in."

Scientists probably have a better understanding 
of how pesticides break down during composting 
than they do of any other class of man-made 
chemicals. When interest in composting yard waste 
as a means of keeping it out of landfills surged 
in the late 1980s, many state and local public 
agencies studied how well composting reduced 
pesticide residue.

Compost pesticide residue consistently proved to 
be so low that most composters today only 
occasionally conduct tests to verify that 
pesticide residue is reduced to the point where 
the compost will not be toxic to plants.

But the low incidence of pesticides in compost 
isn't proof that compost can handle society's 
worst chemicals. The successful elimination of 
pesticide residue in compost is due at least as 
much to regulatory action as it is to microbial 
activity. Since the 1970s, the EPA has banned or 
restricted use of pesticides that persist in the 
environment. Chlorinated compounds, like DDT, 
resist microbial breakdown in both soil and 
compost. The food residue thresholds authorized 
by the EPA for each pesticide help as well, 
placing, by default, a ceiling on the amount of 
pesticide entering composting systems.

The safeguards aren't foolproof. In 1999, 2000 
and 2001, clopyralid -- an herbicide used to 
control broad-leaved weeds in turfgrass, and hay, 
wheat and other crops -- persisted in composted 
lawn clippings at levels high enough to cause 
damage to garden and nursery plants in eastern 
Washington and Idaho. Studies found not only that 
clopyralid breaks down very slowly in compost, 
but also that it is highly toxic to some plants, 
including sunflowers, legumes, tomatoes and 
potatoes, even at residue levels well below those 
allowed for use on turf and grass crops. 
Washington and California banned the use of 
clopyralid on residential lawns and restricted 
use of clopyralid by commercial applicators in 
2002. Since then, no further damage from 
clopyralid residues in compost has been reported.

Even with pesticides that break down rapidly in 
compost, questions remain. Only a small amount of 
pesticide "disappearance" during composting is 
due to mineralization, whereby the compound is 
reduced to water and other inorganic compounds. 
Much of the pesticide volatilizes, vaporizing 
into a gas. Depending upon the compound, the 
vaporized pesticide may or may not pose 
environmental risks. Another large portion of the 
pesticide is adsorbed (or bound) to organic 
matter in the compost. While bound, the pesticide 
is unavailable for uptake by plants; however, as 
the organic matter breaks down further over time, 
the pesticide may again become bioavailable.

As our dependence on compost to both reduce our 
organic wastes as well as to maintain the health 
of our soils grows, composting without a more 
complete understanding of the fate of chemicals 
in compost becomes increasingly risky.

"I believe that composting is the best tool that 
we have for handling many of the different types 
of organic materials that we use," says Richard 
of Pennsylvania State University. "It can reduce 
their impact significantly and at lower cost than 
other options that we have, and we really do need 
to have a society that does a better job of 
recycling its organic matter.

"But we need to look pretty hard at a lot of 
these different compounds. We are depending on 
composting to handle increasing amounts of the 50 
percent-plus of our waste stream that is organic. 
To not be studying these emerging questions seems 
to be pretty naive."

Monterey writer Deborah K. Rich is a frequent 
contributor to Home&Garden. E-mail her at 
home@sfchronicle.com.

http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/05/05/HOGD3PJOUT1.DTL

This article appeared on page F - 5 of the San Francisco Chronicle