Groundwater-borne Diseases Here at Home
When it comes to water, we’re pretty lucky. If you’re reading this, you probably have access to toilets and adequate sewage treatment, and ready access to drinking water that doesn’t make you sick. Somewhere in the early to middle parts of the last century, we solved most of those problems, and then took it up a notch after the Clean Water Act was passed in 1973 so that our sewage wouldn’t (usually) reach our rivers and lakes. There are many members of our human family who don’t enjoy such privileges.
But before we get too comfortable and smug about our water, we should pay attention to what Dr. Mark Borchardt has to say. Borchardt, a research scientist based at the Marshfield Clinic in central Wisconsin, studies groundwater-borne diseases, particularly those caused by viruses, and is coming up with some surprising results. Apparently the United States has about twenty disease outbreaks per year associated with drinking water. More than half of those are from groundwater sources, and that proportion is increasing. Earlier this week Borchardt shared some of the results of his recent studies with us at a Wingspread briefing.
(Aside: In case you want to Google Borchardt, be sure to include the “Dr.” part of his name. As I learned, there is an independent filmmaker of the same name, which whom he is frequently confused. Do you think the filmmaker Borchardt ever gets confused with the virologist Borchardt? It seems only fair.)
Here are a few things I gleaned from his presentation:
· Viruses move through soil farther and faster than bacteria. This is partly because they are smaller, and partly because their surfaces carry negative charges. Since soil particles also tend to be negatively charged, the viruses do not adhere and are carried by subsurface flows. And since many of the pathogenic viruses he studies can live for about two years, they have plenty of time to make their travels.
· Viruses can move through tiny fissures in rocks, and can even get through layers that hydrogeologists have always considered to be impermeable. In Madison, Wisconsin, the public water supply lies beneath an ‘aquitard’, but viruses moving through the sewage treatment plant are routinely found in it. The drinking water is disinfected before distributing, so it’s not a public health concern. But his results were a surprise. (For you non-believers out there, check out Borchardt et. al 2007.Human entericviruses in groundwater from a confined bedrock aquifer. Environmental Science and Technology 41:6606-6612.)
· Small municipal water systems that rely on groundwater are generally contaminated with at least some viruses that cause human illness. Treating the water with ultraviolet light prior to distribution reduces a significant portion of the illness.
· Some contamination is probably coming into the potable water distribution system from the sewerage collection system. In recent work, Borchardt has painstakingly studied the genetic fingerprints of viruses in sewage, and can say fairly definitively that this is happening in the places he’s studied. Probably the best way to address this is to fix the leaking pipes in both our sewerage collection systems and our potable water systems. Some would refer to this as “fixing our crumbling infrastructure.”
· People on private wells seem to not have the same problems as municipal wells. Borchardt thinks this is because most private wells are far enough from sewer lines that they aren’t coming in contact with human viruses.
The work of Borchardt and his colleagues is clearly shaking things up. At least one municipality in Wisconsin (Prairie du Sac) has upgraded its water distribution system to include ultraviolet disinfection as a result of his studies. And I presume that many municipalities, small and large alike, will be thinking about what this means for infrastructure, both the necessity for maintenance and whether or not there are better ways to rebuild.
Note: Shortly after I post this, Dr. Borchardt will be moving his lab to the USDA Agricultural Research Service laboratory, also based in Marshfield WI.