Typically when health or environment officials are looking for confirmation of sewage contamination of a water source, they'll go with indicator organisms as evidence. By sampling the water and looking for fecal coliforms, you can tell whether it has been contaminated by bacteria that typically reside in the gut of warm-blooded animals. There's also fluorescein dye if you're looking to confirm that sewage isn't staying in the ground, but that's only effective if the septic failure leads to wastewater being discharged to the ground surface. In other words, if the sewage is making its way into an aquifer, you're not going to see the dye.
There are a couple of problems with fecal coliforms as indicator organisms: they're not necessarily confirmation of human sewage (i.e. just confirmation of some sort of fecal contamination) and they're not overly persistent in the soil. If you're just trying to tell a water system operator that they've got some contamination issues and need to issue a public notification, they work just fine. But if you're looking to confirm that some actual sewage is getting into the water, you're going to have a hard time in front of a judge.
Researchers from Ontario looked at a wastewater plume from a septic field serving a campground that had been in existence for around 20 years (which, incidentally, is about the life span of the average on-site sewerage system), and note that typical indicators of contamination (besides coliforms) are not necessarily unique to sewage, and therefore don't make the best indicators. Chemical compounds that are unique (ibuprofen, pseudoestrogens, carbamazapine) haven't been studied enough to give a clear indication of how long they persist in the environment. They suggest that artificial sweeteners might have value as a wastewater indicator, since they're unique to human waste, resistant to breakdown in normal sewage treatment, and persist in groundwater.
By setting up a number of piezometers and trace gas sampling points along the wastewater plume from the campground, the researchers were able to not only sample the groundwater for the contaminants of interest, but were also able to perform tritium/helium age dating to identify the age of the wastewater plume. Unsurprisingly, their study showed that once you got about 50m away from the sewage dispersal field area, nutrients and pathogens normally found in sewage were reduced to non-detectable levels. Of the sweeteners tested for persistence, they found that cyclamate and sacharrin appeared to degrade quite effectively, while acesulfame and sucralose concentrations remained relatively constant regardless of distance from the septic tank.
Since the acesulfame was detected in levels nearly 1000x higher than background concentrations in the wastewater plume, and degradation didn't occur over approximately 20 years of sewage system use, it presents itself as a potentially viable indicator for wastewater contamination. Apparently, acesulfame is also added to some animal feed, so it could be used as an indicator of groundwater contamination from manure spreading as well.
There's still some further work to be done, since this is just one study of one onsite sewerage system. However, it shows great potential for a new way of determining whether aquifers are being impacted by nearby wastewater. It's worth noting that, from a public health perspective, there is always the issue of cost when speaking to new indicators. The current culture sampling for pathogens is relatively inexpensive, and provides a "good enough" method of identifying contamination. Moving to a compound that requires some analytical chemistry for identification may just be simply too expensive for publicly funded environmental health organizations.
Source: Robertson, W.D., Van Stempvoort, D.R., Solomon, D.K., Homewood, J., Brown, S.J., Spoelstra, J., & Schiff, S.L. (2013). Persistence of artificial sweeteners in a 15-year-old septic system plume. Journal of Hydrology, 477, 43-54.
Showing posts with label bacteria. Show all posts
Showing posts with label bacteria. Show all posts
2.27.2014
How do we know if our beaches are safe?
I live in the Okanagan region of B.C., which is known for two things: wine and beaches. I might be exaggerating a bit on the "beaches" part, but the Okanagan is certainly a summer destination for a lot of people. The major municipalities and regional districts in the area have done a good job of maintaining public beach access, but with that access comes the risk of exposure to disease-causing bacteria. Historically, the local health authority would be responsible for sampling the water in close proximity to the beach, sampling the bacterial load (coliforms and fecal coliforms), and suggesting a beach closure if any individual sample was above a certain level, or if the running log mean of consecutive samples got too high. In the past couple of years, the local governments have taken on this sampling role but have used the same indicators and tests to determine whether or not a beach is "safe" for public access.
But are culture-based methods of counting coliforms really the best indicator of beach safety, or are there better methods out there? A (very large) group of researchers in the United Kingdom looked at this topic to determine whether molecular methods for enumerating coliform bacteria were better than traditional cultures. They bring up the very valid point that culture-based methods of enumeration can take a couple of days to get results back, whereas molecular methods (like quantitative polymerase chain reaction, or qPCR) can give results in a couple of hours. When dealing with beach water quality for bather safety, the quick turn-around time could be the difference between closing the beach while the hazard exists, and closing the beach once the hazard has already passed (and people have already been exposed to it).
One difficulty the paper points out with the use of qPCR is the current lack of epidemiological evidence between level of exposure and human illness. Because it's a relatively new technique, there isn't yet a strong link between a sample result and the potential for illness like there is for traditional culture counts. They also identify that the specificity of qPCR can be both a blessing and a curse: it's nice to not have to rely on indicator organisms (like E. coli) as catch-alls for human pathogens, but how do you identify the specific pathogens you want to target with the qPCR?
And of course, there's always the cost consideration. Implementing new testing methodologies can be exceedingly expensive, especially when you're talking about molecular biology. Add to that the fact that there would be a necessarily overlap between the two techniques as the transition took place, and you're looking at even higher costs. The researchers argue that the cost increase may not actually be associated with a significant benefit to public health: do people really need "real-time" beach data, or would time and money be better spent building predictive models using existing culture counts?
The researchers came up with a number of recommendations for the UK working group prior to implementation of a molecular method for determining beach safety, but the bottom line is that we're just not there yet. More research and evidence needs to be gathered, and the cost of transitioning to a new methodology needs to be reduced before local governments or health regions will consider the transition (given that there aren't that many concrete benefits).
It's also worth noting that as acute care costs rise, money for environmental health initiatives like beach monitoring necessarily decrease (see: local governments taking on sampling, as noted above). There has to be very real and clear benefits to the program to even keep health authorities involved, let alone getting them to invest new money.
Source: Oliver, David M. et al. (2014). Opportunities and limitations of molecular methods for quantifying microbial compliance parameters in EU bathing waters. Environment International, 64, 124-128.
But are culture-based methods of counting coliforms really the best indicator of beach safety, or are there better methods out there? A (very large) group of researchers in the United Kingdom looked at this topic to determine whether molecular methods for enumerating coliform bacteria were better than traditional cultures. They bring up the very valid point that culture-based methods of enumeration can take a couple of days to get results back, whereas molecular methods (like quantitative polymerase chain reaction, or qPCR) can give results in a couple of hours. When dealing with beach water quality for bather safety, the quick turn-around time could be the difference between closing the beach while the hazard exists, and closing the beach once the hazard has already passed (and people have already been exposed to it).
One difficulty the paper points out with the use of qPCR is the current lack of epidemiological evidence between level of exposure and human illness. Because it's a relatively new technique, there isn't yet a strong link between a sample result and the potential for illness like there is for traditional culture counts. They also identify that the specificity of qPCR can be both a blessing and a curse: it's nice to not have to rely on indicator organisms (like E. coli) as catch-alls for human pathogens, but how do you identify the specific pathogens you want to target with the qPCR?
And of course, there's always the cost consideration. Implementing new testing methodologies can be exceedingly expensive, especially when you're talking about molecular biology. Add to that the fact that there would be a necessarily overlap between the two techniques as the transition took place, and you're looking at even higher costs. The researchers argue that the cost increase may not actually be associated with a significant benefit to public health: do people really need "real-time" beach data, or would time and money be better spent building predictive models using existing culture counts?
The researchers came up with a number of recommendations for the UK working group prior to implementation of a molecular method for determining beach safety, but the bottom line is that we're just not there yet. More research and evidence needs to be gathered, and the cost of transitioning to a new methodology needs to be reduced before local governments or health regions will consider the transition (given that there aren't that many concrete benefits).
It's also worth noting that as acute care costs rise, money for environmental health initiatives like beach monitoring necessarily decrease (see: local governments taking on sampling, as noted above). There has to be very real and clear benefits to the program to even keep health authorities involved, let alone getting them to invest new money.
Source: Oliver, David M. et al. (2014). Opportunities and limitations of molecular methods for quantifying microbial compliance parameters in EU bathing waters. Environment International, 64, 124-128.
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