Variations in setback distances from sewerage systems: one size doesn't fit all

It's often too easy to assign a "safe" setback distance from a source of contamination when considering the installation of a new drinking water source. In B.C., that setback is set forth in the Sewerage System Regulation, and states that an onsite sewerage system can't be installed closer than 30m from a drinking water supply (unless a hydrogeologist is willing to say that there's no risk to reducing it). This distance of 30m, or 100', is fairly common: it's also used by Maine, Massachusetts, California, etc. In a province as diverse and large as B.C., however, this singular measure does not take into account the soil and climate differences that might prevent wastewater from being adequately treated before it makes it to somebody's tap.

After a Norovirus outbreak in Iceland, which was traced back to contaminated drinking water, a group of researchers set out to identify whether there were some considerations for setback distances that weren't being accounted for. The outbreak in question occurred in late summer at a location frequented by tourists and those who owned summer property, with the drinking water being drawn from a well. Due to a few different factors, which will be discussed further on, the minimum setback required for a 9-log reduction in viral load was nearly 900m. That's 30x the setback in the B.C. legislation!

According to this specific study, approximately 1/3 of waterborne outbreaks in affluent nations are due to sewage contamination of groundwater. We assume that a combination of deep drilled wells and relatively slow-moving soils will allow for adequate filtration of the waste water to ensure the effluent entering the aquifer is treated. However, what this doesn't account for are the aspects of soil chemistry that can affect the filtration rate. For instance, viruses travel longer distances in cold groundwater. The groundwater in the Iceland study was around 5'C, which can lead to an inactivation rate for viruses of 1 order of magnitude lower than ground water at 25'C. The researchers point out that not many studies have focused on the relationship between groundwater temperature and viral inactivation.

To properly identify a safe distance between a sewerage system and a well, it's important to consider more than just soil grain size. It's also necessary to look at groundwater temperature, seepage velocity, and soil acidity to determine how long it will take to adequately neutralize the wastewater. The researchers suggest that looking at travel times (e.g. 50 days) may be more reasonable than simply looking at setback distances.

I mentioned above that a 9-log reduction in viral load would've required a setback of 900m in this specific case study. While B.C. legislation has no requirements for reduction of viruses, the Guidelines for Canadian Drinking Water Quality speak to a minimum 4-log reduction of viruses in treatment systems. Since most groundwater systems don't have subsequent treatment (because of their inherent safety), one could attribute a 4-log reduction in soil to being adequate as well. Given all the various parameters that must be considered to determine viral inactivation, it's nearly impossible to say "this setback distance throughout B.C. will lead to a 4-log reduction in viruses".

The summary of this study was that a) the setback distance between the well and the hotel's septic system was inadequate to provide safe drinking water, and that subsequent treatment was necessary, and b) that a lot more research needs to be done to determine how various soil chemistry factors affect wastewater treatment in vivo. Simply saying "it's 30m away, so it's safe" isn't an adequate means of protecting public health, without considering what happens in those 30m.

Source: Gunnarsdottir, M.J., Gardarsson, S.M., & Andradottir, H.O. (2013). Microbial contamination in groundwater supply in a cold climate and coarse soil: case study of Norovirus outbreak at Lake Mÿvatn, Iceland. Hydrology Research, 44(6), 1114-1128.


Food safety in developing countries

I've written a couple of recent articles about street food in developing nations (Brazil and Nigeria, specifically), and the evidence was pretty overwhelming that there's a lack of formal food safety training in these countries, which leads to mediocre food handling practices and increases food safety concerns. A study in Critical Reviews in Microbiology took a broader look at food safety practices in developing countries by performing a thorough literature search, and highlighted some of the concerns with the current system.

One of the first things they pointed out is that food safety is "well recognized" as a primary indicator of economic growth in the developing world. In other words, it's not only important to ensure a safe food supply for health reasons, but also for economic reasons. The cost of health care treatment, missed employment, and lowered production are all financial reasons for improved food safety systems. While countries like the U.S.A. and Canada closely track the economic impacts of food-related outbreaks, and can identify specific numbers of specific illnesses, the researchers found no such data for developing nations. Besides the fact that the majority of food-borne illnesses go unreported (everywhere, not just in developed countries), there's also a lack of formalized surveillance programs in developed countries that could identify these cases and outbreaks. The lack of information is actually representative of a problem unto itself: you can't manage what you can't measure. Without the surveillance systems in place, knowing where to start a food safety program in a developed country would be guess-work, at best.

The authors estimate that 1.8 million children die from diarrheal diseases in developing countries every year. The lack of potable water, adequate medications, and inappropriate hygiene all contribute to an inability to adequately prevent diarrhea from becoming deadly. The lack of post-exposure solutions highlights the importance of preventative systems to ensure diarrhea is not contracted in the first place. Unfortunately, while "improved hygiene, sanitation, and awareness" would lead to reduced illness, death, and economic burdens in developing nations, the fact remains that "poor food supply systems and microbiological contamination" are rampant. Specifically, the authors highlight that "microbiological contamination ... has been identified as a potential cause of food-borne illness in Latin American countries", and that "Argentina has the highest incidence of HUS (hemolytic uremic syndrome) in the world".  They also referenced a study in which Brazilian chickens were analyzed for Salmonella contamination, which found antibiotic resistant strains of S. enteritidis and S. infantis. So, not only does the microbial contamination exist, it exists in a form that would be nearly impossible to quickly and properly treat in developed countries.

Tying in with the street food studies that I've recently written about, Akhtar, Sarker, & Hossain point out that "street vending of foods is believed to be a potential cause of illness and thus needs to be precisely focused". This echoes what the other studies have suggested as well: street food brings about some unique challenges to safe food handling, and hazard management needs to be able to mitigate these specific dangers. When considering the economic benefits of street food that were identified in Nigeria & Brazil, this paper's commentary on the detriments of food-borne illnesses to developing nation's economies makes even more sense. In these nations where street food is considered a great way for females to make money and provide for their families, lack of controls and food safety programs could derail the entire system.

So, while it's clear what needs to be done, why hasn't it happened yet? Akhtar et al indicate an "absence of political commitment, intervention of international agencies, awareness, and strict legislation". Political commitment is clearly one of the most important first steps that needs to occur, however. Agencies like the UN and WHO are unable to provide anything more than information and basic guidance unless the leaders of these developing nations are willing and able to commit to specific food safety programs. Education, legislation, and funding for enforcement all need to be in place before change can occur. It may be a difficult sell to convince poor nations to provide funding to preventative measures, but with further research into the true economic cost of food-borne illnesses in developed countries, a strong case could be made that prevention is the best medicine.

Source: Akhtar, S., Sarker, M.R., & Hossain, A. (2014). Microbiological food safety: a dilemma of developing societies. Critical Reviews in Microbiology, 40(4), 348-359.