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We’re making a mess in our forests with our sewage sludge

May 25, 2016
By Richard Honour and Steven R. Vincent
For Environmental Health News

SNOQUALMIE, Wash.—Out in the Snoqualmie forests of eastern King County, on the west side of the Cascades, the ground is black and mucky. It’s an unnatural scene with a toilet-bowl stench.

And it comes from tons upon tons— about 120,000 tons a year—of sewage sludge that King County, home of Seattle and more than 2 million people, disposes of annually in these forests and on farms and rangelands of central and eastern Washington.

This sludge, known euphemistically as “biosolids,” consists of semi-liquid waste obtained from the processing of municipal sewage. The goal of this process is to obtain clean water to release into the environment, and thus, the cleaner the water, the more toxins and contaminants are retained in the sludge. This sludge used to be dumped into the ocean, but because of its toxicity this process is banned. Instead we now spread it in our forests and on our agricultural lands.

The spreading of this sludge carries considerable risk and should be stopped. As scientists, we are increasingly concerned with this reckless practice.

An unimaginably large number of chemical and biological contaminants exist in sewage sludge, and many persist for decades after disposal. Scientific investigations have identified only a tiny fraction of the total contaminant load. We cannot describe with any confidence the true range of contaminant risk from the sludge. Call it an “unknown unknown.”

But we get an idea of the potential synergistic interactions from the contaminants that we do know.

To illustrate the difficulties, take just one group of persistent, bioaccumulative, and toxic compounds known to be in sewage sludge at high concentrations: brominated flame retardants. Perhaps the most well known sub-class of the brominated flame retardants are called polybrominated diphenyl ethers (PBDEs). There are 209 different PBDEs, each of which has a unique toxicology and environmental fate.

Our initial analyses—not yet published—revealed high concentrations of PBDEs in the soil and water of forests “treated” with sludge.
PBDEs have been studied around the world for several decades, yet we still have a poor understanding of the true risks from their release into the environment. We have, for instance, no definite information on how PBDEs affect human health. But research on laboratory animals suggests an array of adverse health impacts, including thyroid hormone disruption, delayed puberty, learning impairments and behavioral changes.

Not surprisingly, we also find polychlorinated biphenyls, or PCBs, compounds the U.S. Environmental Protection Agency banned in 1979 because of their lengthy residence time in the environment and their link to cancer and birth defects in lab studies. The PCB family also has 209 different members, all with varying degrees of toxicity. There are another 210 chlorinated dioxins and dioxin-like “congeners,” also found in some sludges.

These are just the contaminants we have identified. To refer to our current knowledge as the tip of the iceberg would grossly overestimate what we actually know.

Meanwhile the sludging continues. The sludge is hauled by tandem dump trucks into the forest via old logging roads, where it is dumped into skids and then loaded into spreaders.

Credit: Richard Honour

These monster vehicles drive along secondary access trails while slinging the sludge up the trees, as high as 35 feet up and into the forest. They often hit the streams and wetlands in the process, because drivers cannot see what they are doing. It is a mess, with uncontrolled rates of application.

Rain spreads the sludge into and across the forest soils, drains it into numerous streams and wetlands, ultimately carrying the contaminants into the Snoqualmie River and other waters, and on to Puget Sound.

The mass killing is difficult to comprehend. This sludge kills many forms of wildlife: snakes, lizards, newts, insects, moles, shrews—a clear case of ecosystem disruption. The sludge attracts masses of flies, gnats, mosquitos and other insects, which breed in the sludge and in the sludge puddles and pools, and then die from the contaminants. It is toxic waste.

The science surrounding sewage sludge is unacceptably sparse. Either the reviews are out-of-date and incomplete, failing to account for all that we do know about emerging contaminants and what we don’t know, or they are written more as promotional materials for the sludge disposal industry in an attempt to sell the product.

We must stop this madness. Municipalities and regional sewage districts look eagerly at the revenue stream from selling their sludge. An entire industry has sprouted—Big Sludge—to market and sell this allegedly “non-toxic” resource. They fail to disclose to taxpayers the considerable risks from the contamination of lands and waterways. The science does not agree with this oversimplification.

Out in the Snoqualmie forests, a deep, oily, wet layer of sludge has sealed the soil in this patch of woods. The vibrant soil microbiology has gone anaerobic, generating methane and other greenhouse gases. A video shows the bleakness; pardon the sneeze in the middle—the fumes are overwhelming.

As sickening as this stench is, the denial of state, regional and county officials who fail to take a precautionary approach to biosolids is every bit as nauseating. We will all pay for this in the long run.

Richard Honour is the executive director for The Precautionary Group, a Washington state-based company formed to evaluate the adverse effects of sewage sludge and other toxic wastes on human and environmental health. Steven R. Vincent is a professor in the Department of Psychiatry at the University of British Columbia.

EHN welcomes republication of our stories, but we require that publications include the author’s name and Environmental Health News at the top of the piece, along with a link back to EHN’s version.

For questions or feedback about this piece, contact Brian Bienkowski at


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