Spring 2009

Living Science

Sharon Long shows off a water sample turned pink by lab tests, indicating the presence of coliform bacteria.

SHARON LONG is an associate professor of soil science in CALS, but that title only hints at her multidimensional role for the university and the state. As director of environmental microbiology for the Wisconsin State Laboratory of Hygiene, Long runs a public-service unit that analyzes some 60,000 water samples each year, part of the state’s effort to keep its wells and drinking water safe from microbial contamination. As if that weren’t enough to keep her busy, she has appointments in UW – Madison’s Nelson Institute for Environmental Studies and the College of Engineering’s civil and environmental engineering department.

What’s with all of your titles?

Well, my work is very interdisciplinary. When you’re talking about tracking pathogen sources in water-and keeping them from reaching people-you need access to people with a bunch of different backgrounds. You need people who understand microbiology. You need people who understand public health. You need people who understand laboratory testing. And you need people who can solve problems. One of the things I really like about Wisconsin is that it’s so interdisciplinary by nature. I can have a foot in all of these camps and hire students from each of those areas.

Your work with the State Laboratory of Hygiene is very applied. Is it common for a professor to have that role?

Yes, that’s been the tradition. The lab is technically part of the university, and they always try to have a strong connection to the research community here. My role is really to bring in the research perspective-to bring in the tools that allow us to figure out what might be making a water sample unsafe and how the pathogens got there.

Where do the samples come from?

All over the state. The lab is a client-based service, and so anyone can send a sample in to be analyzed. We get a lot of samples from private well owners who want to be sure that their well hasn’t been contaminated by animal waste or other things. And we also test for a number of municipalities, including Madison and Milwaukee.

Is this routine testing, or are you investigating problems?

It can be both. For instance, we did a lot of testing after the floods last summer. When people came back to their homes, many were worried about flood waters going over the tops of the wells, and a fair number of those tests did come back unsafe.

What happens then?

Well, in that case, we worked with the Department of Health and Family Services and the Department of Natural Resources to get information out to people in the affected areas. Generally, the first thing they do is super-chlorinate the well and pump it through. Then, if it comes back contaminated again, we try to find out what’s in there and where it may be coming from. We start looking to see if there’s a continuing source of contamination.

And that’s where your research comes in.

Right. The first level of testing generally just tells you about the presence or absence of coliform bacteria, which we use as a broad-level indicator because they live in almost every warm-blooded animal. So that test tells us that we may have some kind of contaminant getting into the water supply. Then the question becomes what kind of contamination we’re dealing with and in what quantity. There is a standard set of microorganisms we can look for, and that’s the path that pretty much any public-safety lab would follow.

But if the question becomes about more than just identifying the particular pathogen, we do have some tools that allow us to start to figure out where the pathogens came from. The field is called microbial source tracking, or MST. We have tests that can tell us whether the source of the pathogen was human or non-human, and there are even some tests that allow us to go deeper than that and ask what kind of animal was the source of the contamination. For example, we can do a test where we discriminate between grazing animals and all other animals, which could tell us if the contamination was coming from a nearby farm or some other source.

How can you tell?

Every species of animal has a unique intestinal environment and therefore a unique mix of microorganisms that live in that environment. The idea is to use some high-level microbiology to identify differences in the microorganisms that can tell us where they lived. So if we have contamination in a new residential development that is located next to an active swine farm, you want to look at those microorganisms and figure out whether they came from humans or pigs. If it’s humans, you would want to look at the septic system as a likely source of contamination, but if it’s pigs, you’d try to see if animal waste was contaminating the water supply.

It sounds like CSI.

It is. But really, it has only been within the past 10 years that science has progressed enough to do this. People have been studying source tracking since the 1970s, but we’re finally getting to the point where we can apply it with some level of certainty.

I understand you’ve used this technology recently in a contamination problem at a restaurant in Door County. Can you tell me more about that case?

Yes, that was really fascinating. This was a brand-new restaurant in one of the popular vacation areas up there, and not long after it opened, a number of people got sick. The concern was that since there was a lot of agriculture in the area that maybe there was contamination from animal waste. But when we applied our source tracking, we found human markers, meaning that it had to be a human source. It turned out that a pipe from the septic holding tank was not hooked up properly, and the sewage was going straight down into the aquifer and reaching their well.

Do you think pegging the source as human helped identify that problem?

Certainly, because it put the focus on the septic system. It was a brand-new system, and it was very well designed, so there wasn’t much reason to suspect it would be a problem. But the test caused the county to go back and reevaluate it. I hear the restaurant has since put in a state-of-the-art system for treating its well water. They’ve probably got the cleanest water in Door County now.

That’s good news. But seeing all these cases of contamination-does it ever make you think twice about drinking tap water?

Not at all-at least not in this country. One of the societies I belong to is the American Water Works Association, and at their annual conferences they actually pay extra to make sure that all of the water bottles are filled with tap water. We’ve got great water, and I never think twice about it.

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