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By Peter Montague

In the mid-1980s, a citizens' organization in New Jersey — Clean Ocean Action, led by Cindy Zipf — launched an aggressive campaign to protect the oceans from the dumping of toxic sewage sludge. They were up against extraordinary power: the US Environmental Protection Agency (EPA), New York and New Jersey environmental officials, nearly every municipal government. But they persevered and won.

Thus in the early 1990s, municipalities had to find other places to dump their sewage sludge.

Sewage sludge is the material that remains after bacteria have digested human wastes. If human wastes were the only substances entering the sewage treatment plant, then sewage sludge would contain only nutrients and should be returned to the land.

Unfortunately, most sewage treatment plants receive industrial toxic wastes, which are then mixed with the human wastes, creating a poorly understood mixture of nutrients and industrial poisons. Furthermore, many cities have built systems that mix toxins from storm water run-off with the sewage.

As a result, sewage sludge contains a strange brew of nutrients laced with low levels of PCBs (polychlorinated biphenyls); dioxins and furans; chlorinated pesticides; carcinogenic polynuclear aromatic hydrocarbons (PAHs); heavy metals; bacteria, viruses, parasitic worms and fungi; industrial solvents; asbestos; petroleum products.

American industry uses roughly 70,000 different chemicals and any of these can be found in sewage sludge. In addition to the original chemicals, unique metabolites and degradation products develop anew in sludge. To give but one example: trimethylamine can be converted to the powerful carcinogen, dimethylnitrosamine.

The US produces 5.3 million metric tonnes of sewage sludge each year (dry weight, not including the water that carries it). Today about 16% of US sewage sludge is incinerated, and the ashes are buried in landfills; 38% of sludge is landfilled directly; 36% is spread onto farmland or forest land or otherwise mixed into soils; and 10% is handled in other ways (piled on the land and abandoned, for example).

The sewage treatment industry — and the municipal governments that employ them — are a powerful political force. Together in the late 1980s they figured out that the cheapest thing to do with sewage sludge is to spread it onto or into the land, preferably as close to its point of origin as possible, to minimise transport costs.

However, there were obstacles to overcome. Few people thought sewage sludge sounded good as fertiliser for food. So the industry hired a public relations firm, Powell Tate, and renamed sewage sludge "biosolids". They convinced the EPA to go along with this verbal detoxification. The Federation of Sewage Works Associations also renamed itself — it is now the Water Environment Federation.

The scientific literature on sewage sludge is large, but much of it consists of articles intended to break down public resistance to the use of sewage sludge on farm land. Nevertheless, there is a core of serious research. In recent months, we have examined this literature, and here is what we found:

• Sewage sludge is mutagenic (it causes inheritable genetic changes in organisms), but no-one seems sure what this means for human or animal health. In its regulations, EPA has simply ignored this information.

• Two-thirds of sewage sludge contains asbestos. Because sludge is often applied to the land dry, asbestos may be a real health danger to farmers, neighbours and their children. In its sludge regulations, EPA does not mention asbestos.

• EPA issued numeric standards for 10 metals. However, the movement of metals from soils into ground water, surface water, plants and wildlife — and of the hundreds of other toxins in sludge, which EPA chose not to regulate — are poorly understood.

• Soil acidity seems to be the key factor in promoting or retarding the movement of toxic metals into ground water, wildlife and crops. In creating its regulations, EPA assumed that sludge-treated land would be under the perpetual care of a farmer who would lime the soil to keep it alkaline and prevent the metals from moving dangerously.

But in the real world, farmers go out of business while acid precipitation keeps soaking soils with dilute acid year after year. A build-up of toxic heavy metals in soil today seems to be a prescription for trouble 30 to 50 years down the road.

The National Research Council (NRC) of the National Academy of Sciences gives sewage sludge treatment of soils a clean bill of health in the short term, "as long as ... acidic soils are agronomically managed". However, the NRC acknowledges that toxic heavy metals and persistent organic pollutants can build up in treated soils. If such a build-up occurs and the soils are no longer "agronomically managed", what will happen then?

• Research clearly shows that, under some conditions (which are not fully understood), toxic metals and organic industrial poisons can be transferred from sludge-treated soils into crops. Lettuce, spinach, cabbage, Swiss chard and carrots have all been shown to accumulate toxic metals and/or toxic chlorinated hydrocarbons when grown on soils treated with sewage sludge.

• In some instances, toxic organics contaminate the leafy parts of plants by simply volatilising out of the sludge.

• There is good reason to believe that livestock grazing on plants treated with sewage sludge will ingest the pollutants. Sheep eating cabbage grown on sludge developed lesions of the liver and thyroid gland. Pigs grown on corn treated with sludge had elevated levels of cadmium in their tissues.

Cows, goats and sheep are also likely to eat sludge directly. In grazing, these animals may pull up plants by the roots and thus ingest substantial quantities of soil. A cow may ingest as much as 500 kg of soil each year.

• Small mammals have been shown to accumulate heavy metals after sewage sludge was applied to forest lands. Shrews, shrew-moles, and deer mice absorbed metals from sludge. Insects in the soil absorb toxins, which then accumulate in birds.

• Sewage sludge applied to soils can increase the dioxin intake of humans eating beef (or cow's milk) produced from those soils. Humans in the industrial world already carry unsafe burdens of dioxin in their bodies, according to EPA.

• Sewage sludge is produced in huge quantities day after day, year after year. Municipalities find themselves under relentless pressure to get rid of the stuff. It is exceedingly expensive to treat it to clean it up. Towns and cities have every inducement to cut corners, skimp on tests, fudge the numbers, claim that their sludge is cleaner than it really is. Farmers have no capacity to analyse sludge independently; they must rely on the word of the sludge supplier.

Only an aggressive, independent oversight agency can protect public health. Where can such an agency be found?

[From Like Â鶹´«Ã½ Weekly, Rachel's is a non-profit publication which distributes information without charge on the internet and depends on the generosity of readers to survive. If you are able to help keep this valuable resource in existence, send your contribution to Environmental Research Foundation, PO Box 5036, Annapolis, Maryland 21403-7036, USA. In the United States, donations to ERF are tax deductible.]