A Primer on Emerging Contaminants

By Alan S. Kolok, Ph.D.
Department of Biology, College of Arts and Sciences,
University of Nebraska, Omaha

Dr. Alan S. Kolok

We’ve all seen the headlines: pharmaceutical compounds in drinking water, reproductive abnormalities in male fish downstream from wastewater treatment plants, agrichemical pesticides feminizing male frogs, and the list goes on.

Fortunately, most of the newspaper headlines relate to distant parts of the country far removed from Nebraska. Still, the headlines leave us uneasy; are these issues relative to Nebraska, might these contaminants influence human health, and if so, what, if anything should be done about it?

In this and upcoming issues of the Water Current, we’ll take a closer look at the issue of ‘emerging contaminants’ particularly focusing on recent findings from scientific literature and on topics that are directly germane to Nebraska.

The term “emerging contaminant” is a confusing one in that the compounds aren’t necessarily emerging onto the contaminant radar screen. Nevertheless, while the name may very well be a poor choice, it has become part of the modern lexicon (in fact it even appears in the UNL Water Center’s list of Nebraska’s Top-10 Water Challenges!) and we appear to be stuck with it for some time.

The U.S. Geological Survey (USGS) defines emerging contaminants as chemical and/or microbial constituents that have not historically been considered to be contaminants. They go on to suggest that sources for these contaminants can be municipal, agricultural and industrial, and that these compounds may require shifts in our traditional thinking about contaminants.

How emerging contaminants are forcing paradigm shifts in toxicology warrants closer attention.

In toxicology, it is axiomatic that ‘dose makes the poison’. In fact the root of this expression can be traced all way back to Paracelsus (1493-1541) who is often credited as being the “Father of toxicology.” 

Indeed, most of us have a relationship with doses of toxic compounds that parallels 1970’s Supreme Court Justice Potter Stewart’s feelings on obscenity….we may not be able to quantify what it is, but we certainly know it when we see it!

Our inherit understanding of what is, and is not toxic, in the case of emerging contaminants, can be incredibly misleading. Some emerging contaminants are toxic at levels so low that their continued biological effect appears to stretch the imagination.  It has been reported that concentrations of emerging contaminants are biologically active at concentrations in the part per billion (ppb) range.

To put this in perspective, consider that one ppb is equivalent to a teaspoon of liquid poured into an Olympic-size swimming pool.  How can such low concentrations of a compound result in adverse biological effects?

It’s important to recognize that some emerging contaminants either mimic, or are, biological signaling molecules. Signaling molecules, such as hormones, travel in the blood and cause activation of cellular processes, and they do their jobs at remarkably low concentrations.

The naturally occurring estrogen, 17b-estradiol, which is responsible for sexual development in females (women and fish alike) is doing so at levels that average about 100 ppb. Clearly, signaling molecules manifest dramatic effects at astonishingly low concentrations! 

If a male, (again, humans and fish alike) is exposed for prolonged periods to exogenous estrogen (or compounds that mimic estrogen) it is not all surprising that feminization (or demasculinization) may be the outcome.

A further complication associated with emerging contaminants is that there may be no ‘no effect’ dose.

Again, taking our cue from classic toxicology, if dose does indeed make the poison, then there ought to be a dose below which no adverse effects occur.  Once again, this need not be true when dealing with biological signaling molecules (or molecules that mimic them). The reason is obvious, if signaling molecules already exist within the bloodstream, then any exogenous addition to that baseline concentration of these molecules can very well have effects on the signals these molecules are sending.

So where does this leave us?

Some emerging contaminants are (or can mimic) our very own biological signaling molecules. Furthermore, these molecules (often termed endocrine disrupting compounds) can manifest their effects at astonishingly low concentrations.

While not all emerging contaminants are endocrine disruptors, the low dose paradigm may apply to many other biologically active compounds, including exogenous pharmaceuticals.

In the next installment, we’ll take a closer look at pharmaceutical compounds, what they are, where they come from and why they are a growing concern.