Depending on the level of treatment and thus the cost of delivered water, various contaminants and pathogens can be left in and ignored, or removed and acknowledged. Under some circumstances, the water can be considered as “legal” but that may still beg the issue of its being safe. This, then, bespeaks of a complex issue that bears much more discussion than allotted here.
Removal of pathogens and their genes relates, in part, to the screen and membrane size to control pass through of things like antibiotic resistant genes and on the differences between indicator microbes and some of the contaminants. Some thought and discussion is warranted. Why this? First, the genes are designed small enough to be extruded through the bacterial pilus, the tube connecting to bacteria during coupling, a tube with in internal diameter of about 2 nanometers (2nm). A virus can squeeze through about 30nm. That takes the treatment train down to a fairly sophisticated level. The standard coliform bacteria, as used to test water, is about 2000nm long and about 500nm in diameter. This is why when one looks for antibiotic resistant genes, or that matter, virulence factors, as found in tertiary treated recycled water, it becomes obvious that this level of filtration is insufficient treatment. So, how small do we need to go? Probably down to reverse osmosis, hence high cost. Is the water being delivered going to be RO?
Tests using the now antiquated standard coliform will not do. Tests on one of the most modern wastewater treatment plants in the U.S. showed an abundant output and release of antibiotic resistant genes. They are much more resistant to control than the indicator bacteria. And, tests on indicators fail to appreciate the stealth state of bacteria, known as the viable but non-culturable (VBNC) state. In the VBNC state, these bacteria—-the ones used for standard indicators—don’t show up on the state’s tests. So, the tests results can be false negatives. Further, while passing down the pipe, say toward the crop of leafy greens to be irrigated, these bacteria in the VBNC state can resuscitate and by the time they reach the sprinkler head, their numbers are off the charts——-not good. But, because they entered this stealth state, they could not be seen on the standard test.
Thus, the way to be sure is testing where the water is used, not as it first leaves the treatment works because of VBNC, but at the sprinkler head or spigot. Well, some might say, “so what, these are only genes, not the pathogens”. But testing does show a resuscitation of the stunned bacteria if one bothers to check the end of the pipe. Through gene swapping, bacteria can, in a single gene transfer, become lethal pathogens. Unless the end of the pipe is tested turning your gut bacteria into pathogens can happen with a glass of water, or a leafy green irrigated with recycled water. The scientific literature has an abundance of papers on this.
Are the water agencies and others proposing this willing to test for resistant bacteria and genes, especially at the end of the pipe?
Dr Edo McGowan
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