A Letter on SLUDGE from Professor David Pimentel
SUMMARY: "Although sludge might be viewed as a beneficial resource with valuable nutrients, the risks of applying the sludge to agricultural lands has too many risks for the available benefits."
Cornell University/College of Agriculture and Life Sciences
I understand that you are considering legislation concerning regulations on the use of sewage sludge. For several years, I investigated the potential of sewage sludge for use on agricultural land for crop production. My graduate students and I used sludge from Syracuse, NY (contaminated sludge) and Cayuga Heights, NY (uncontaminated sludge from a residential area with only one tiny industry).
We grew crops in both sludge types and assessed the growth of the crops and abundance of beneficial and pest insects on the sewage treated crops. In the first experiments, we found that insect populations were significantly reduced on the Syracuse sludge, similar to as if it has been treated with a systematic insecticide. In the first experiment, the crops and insects did well on the Cayuga Heights sludge.
However, subsequent experiments using sludge from the same locations, we found the crops and insects responded similar to the first experiments. What was unexpected was that the crop plants did poorly and the insects were negatively influenced by some unknown chemical(s) in the Cayuga Heights sludge. We consulted a toxicologist but did not have sufficient funds to conduct an investigation of the chemical pollutants that were NOT supposed to be in Cayuga Heights sludge. This illustrates the problem with sludges-one batch may be alright for agricultural use but the next may not be. Needless to say we never ate any of the crops produced on fields with either the Syracuse sludge or the Cayuga Heights sludge.
We also fed earthworms on Syracuse sludge and then fed Japanese quail the contaminated earthworms. We found that the earthworms concentrated one of the heavy metals, cadmium. This metal was found to be toxic to the quail. It is quite possible that this and other heavy metals commonly found in sludge will be toxic to other bird species that feed on contaminated earthworms.
Sludge also may contain metals from city water. For instance, we found that we could not use the water from Cayuga Heights to raise some snails because of the copper in the tap water. More that 99% of the water pipes in Cayuga Heights have copper piping. Copper is leached from the pipes at sufficient levels to be toxic to some snails that are highly sensitive to copper. Of course, the copper will accumulate in the soil and eventually be toxic to crops and other plants.
The hazards of using sludge is that the toxicants may be tolerable in one batch of sludge but not in another. In addition, chemicals like copper in time will accumulate in the soil and be toxic to crops and plants. Once the metals contaminate the soil, it is impossible to cleanse the soil of the pollutants.
Although sludge might be viewed as a beneficial resource with valuable nutrients, the risks of applying the sludge to agricultural lands has too many risks for the available benefits.
I hope that my scientific research and experiences with sewage sludge is of help to you.