So what happens if you release untreated sewage to the marine environment?

Male' Swimming Tract Area(Source: Kamil Lukasik; google + )

Recently, I had been given the opportunity to analyze water quality results from tests conducted by a private firm close to sewage outfalls in Maldives. It is common knowledge disposal of raw sewage is 'bad' for the environment and human health. But is it really the case?

One of the cases at hand was that of the famous outfall near swimming track area in Male'. Unfortunately, I was not the one to design the sampling survey and I found it rather lacking, to say the least. One sample close to outfall (about 10m) was collected and tested for T. Coliform, F. Coliform, nitrates and phosphates. Even though I cannot reveal actual results due my agreement with our client, all I can say is, in terms of  mineral content of the sample, it was surprisingly low (within levels of unpolluted sea water; hence no cause for eutrophication). However, there were moderate amounts of fecal and total coliform. The question is, where exactly was the sample collected? According to the information I received, it was just outside the housereef, away from the swimming track. 

So is it bad to find F.coliform in this sample? Many studies exist on the affects of saltwater on fecal indicator bacteria (Anderson 2005, Anderson 1979, Barcia-Lara et al. 1991, Ferguson 2005) and scientists are in agreement that saltwater eliminates fecal indicator bacteria. Studies have shown a combination of the biological, chemical and physical makeup of saltwater all affect the presence of indicator bacteria (Anderson 2005). A study conducted by Iris Anderson shows that the higher the salinity, the more stressed the sample of E. coli becomes (Anderson 1979).So basically, saltwater kills fecal coliforms, if in appropriate limits. Therefore, it is safe to say, if the outfall is located in a suitable location (based on strength of currents in the area and amount of sewage released), there will not be any significant effect on the environment or people swimming close to it. So what about the one at Male' swimming track? Well, I am not sure. I need to know strength and direction of currents, a reliable water quality test result of effluent, a bunch of more sea water quality results at the outfall location. 

All I can say after this is, I wouldn't swim at the track if I were you... The available information suggest, the sample was collected from a location outside the area currents are carrying sewage, hence the reduced concentration of minerals; which also suggest, the area, currents are carrying most of the stuff released from the outfall would be the swimming track area... ouch! If there was a moderate amount of f. coliform in this sample, just how much would be in the swimming tract? Depends on the currents again; if currents are strong enough to carry the bacteria inside the swimming tract area fast enough before they are killed off from high salinity, there will be a lot of bacteria in that water and you seriously wouldn't wanna swim there.

What exactly are 'coliforms' in a water quality test? Total coliforms are just a group of rod-shaped Gram-negative non-spore bacteria which can ferment lactose with the production of acid and gas when incubated at 35-37 degrees. They are found in almost all aquatic environment, soil and on vegetation. They are present in feces of warm-blooded animal and are themselves not normally causes of serious illness. Their presence is used to indicate presence of other dangerous parasites/ bacteria. Fecal coliform is a subset of total coliform and is potentially hazardous to human health.The presence of Fecal Coliform bacteria or E. coli indicates contamination of water with fecal waste that may contain other more harmful or disease causing organisms. Ingesting significant amounts of water contaminated with these organisms can cause stomach and intestinal illness including diarrhea and nausea, and even lead to death. These effects may be more severe and possibly life threatening for babies, children, the elderly or people with immune deficiencies or other illnesses.

What about the environment? The most significant impact of releasing sewage to the marine environment would be that of increasing nutrient levels in the water; particularly nitrates, phosphates and such. This promotes plant growth and can trigger an algal bloom if in high concentrations; resulting in a significant reduction in dissolved oxygen level of the water at these locations. Consequently, marine life such as fish and coral could potentially die out rapidly from suffocation depending on the extent of oxygen depletion. This is also known as eutrophication. There is also potential for pollution of the the environment by contaminants such as heavy metals, detergents and similar compounds present in the sewage. These are harmful to wildlife though not as significant as eutrophication. In most cases, the concentration of these compounds/minerals in waste water are diluted by mixing with the water body. A good current and wave action at discharge location will dilute these compounds to low enough levels for them to be insignificant in the environment; hence no consequent adverse effect on the environment. However, in case of Male' the amount of sewage released to the environment and strength of currents at outfall locations suggest appropriate dilution rates are unlikely to occur, hence there is potential for severe environment deterioration at these locations.


Further water quality analysis and examination of the environment at outfall locations need to be carried out before going all ape-shit on the government. 


References;

• Anderson, I. C., Rhodes, M., and Kator, H. 1979. Sublethel Stress in Escherichia coli: a Function of    Salinity. Applied and Environmental Microbioloby. 38:1147-1152.
• Anderson, K.L.,Whitlock J. E. and Harwood, V. J. 2005. Persistence and Differential Survival of Fecal Indicator Bacteria in Subtropical Waters and Sediments. Applied and Environmental Microbiology. 71:3041-3048
•  Barcia-Lara, J., Menon, P., Servais, P and Billen, G. 1991. Mortality of Fecal Bacteria in Seawater. Applied and Environmental Microbiology. 57:885-888
• Ferguson, D., Moore, D., Getrich, M. and Zhowandai, M. 2005. Enumeration and speciation of enterococci found in marine and intertidal sediments and coastal water in southern California. Journal of Applied Microbiology 99:598-608.