Safe Drinking Water & Basic Sanitation

Water and sanitation

One of the goals of the Millennial Development Goals (MDG) was to globally reduce by half the number of people without access to safe drinking water and basic sanitation by 2015. According to WHO & UNICEF (2015), only the drinking water target was met however most countries in Sub-Saharan Africa did not meet this target. The MDG sanitation target was not met. It is estimated that close to 663 million people lack access to improved drinking water sources and are using unprotected wells and surface waters, half of them from Sub Saharan Africa (WHO & UNICEF, 2015). The number of people worldwide without improved sanitation is also high (2.4 billion people) with the majority of them from South Asia and Sub-Saharan Africa, most of them people still practicing open defecation. Approximately 946 million people are still practicing open defecation (WHO &UNICEF, 2015).

Unsafe drinking water is caused by contamination of water. Contaminants include both microbial and chemical contaminants with groundwater being less vulnerable than surface waters (Fawell & Nieuwenhuijsen, 2003). Poor sanitation in most cases is the source of microbial contamination of water. Pathogenic microorganisms are known to survive and grow in low nutrient aquatic environments such as surface waters. Nearly all human pathogenic microorganisms are heterotrophs, they utilize Dissolved Organic Carbons (DOC) as their source of carbon and energy (vital, 2010). Contaminated water can therefore transmit these pathogens and pose huge health risks to people dependant on surface waters such as rivers, streams, and lakes. The same water that is essential to life might be a source of infections and death to many people living in Sub Sahara Africa. Waterborne diseases It is known that waterborne diseases are diseases spread through water with water acting as the passive carrier for the infecting pathogens. It is estimated that more than 1.5 million children die yearly from diarrheal diseases (Fenwick, 2006).

Ingestion of pathogen contaminated water might lead to diseases like cholera, typhoid, bacillary dysentery, gastroenteritis, infectious hepatitis, leptospirosis, giardiasis among others. Pathogens causing these diseases include bacteria (Salmonella typhi, Shigella spp, Vibrio cholera, Escherichia coli, Leptospira spp, Campylobacter jejuni), Viruses (Hepatitis A, Rotaviruses), and Protozoa (Entamoeba histolytica, Giardia lamblia, Cryptosporidium homonis). Cholera is known to be caused by Vibrio cholerae which is endemic to freshwaters zooplankton (Reidl & Klose, 2002). Cholera is characterized by extensive diarrhea which leads to possible dehydration and deaths occur in 50-70% of untreated cases (Ashbolt, 2004). In Kenya, the highest cases of cholera outbreak were reported between 1997 and 1999 where 33,400 cases were reported.

In 2009, 11,679 cases were reported with 279 casualties throughout the year, the peak being during the rainy season between March and June (WHO, 2010). Typhoid is known to be transmitted from person to person due to fecal contamination of food or water with the causative agent being Salmonella entorica serovar Typhi (Mogasale, et al., 2018). Symptoms are known to begin 1 to 6 weeks after exposure include high fever, diarrhea, fatigue and constipation with fatality ratios ranging from 10 to 30% if untreated. An estimate of about 21 million people globally are affected by waterborne typhoid and paratyphoid fevers (Crump et al., 2004). To prevent such diseases it’s essential for people living in Sub-Saharan Africa to have access to safe drinking water and improved sanitation. Water contaminants Contaminants are known to be any chemical, physical, radiological, or biological substance in water. Fawell & Nieuwenhuijsen (2003) describe chemical contaminants as comprising of metals (arsenic, iron, manganese, selenium, and uranium) and other elements and compounds including fluorides and agricultural pesticides.

Chemical contaminants are known to cause certain health effects including cancer, neurological disorders, cardiovascular diseases and miscarriages (Calderon, 2000). Biological contaminants include microorganisms such as bacteria, protozoa, and viruses, most of them from sewage systems and fecal contact with water. They are the largest cause of waterborne diseases in the world (Villanueva et al., 2014). To access clean drinking water it’s necessary to decontaminate water. Water decontamination methods Chlorination is considered to be the dominant method of water disinfection. Chlorine and its compounds are known to be strong oxidants and effective microbicides against most pathogenic microorganisms. It is considered inexpensive and widely available for use, however, it has several limitations since it produces disinfection byproducts (DBPs).

Chlorine is known to form hypochlorous acid and hypochlorite with water which then reacts with natural organic compounds to form halogenated products like haloacetic acids, trihalomethanes, and chlorophenols (Nieuwenhuijsen et al., 2000). Studies have shown that certain DBPs cause kidney, liver and colon cancer, adverse reproductive and development effects (Boorman, 1999; Nieuwenhuijsen et al., 2000; Villanueva et al., 2014). Ozonation is another known form of water disinfection. Ozone is known to have high oxidation potentials and is able to cause cell membrane rupture in bacteria and viruses. Use of ozone is known to be a costly method. Ultra Violet treatment (UV) is another known method for water disinfection. UV energy of certain wavelengths is known to affect double bonds between two carbons (Cutler, 2011). Unsaturated organic compounds responsible for cell reproduction and cell metabolism such as purine, flavins, and pyrimidine are affected.

Nucleic acids containing these bases such as DNA and ribonucleic acid (RNA) are also affected (Cutler, 2011). They undergo molecular transformations and through these microorganisms are inactivated. Membrane filtration methods such as ultrafiltration, microfiltration, and reverse osmosis are also used in water decontamination. They use pressure to move water through a semi-permeable membrane. Contaminants including microorganisms are filtered out by the membrane while water moves through it. Studies have however shown that microorganisms especially bacteria are not rigid but are deformable and may be able to penetrate small pore size membranes (Gaveau, 2017). It is known that due to their inability to kill microorganisms, this method ought to be applied with other methods such as UV treatment. Modern methods of water disinfection against pathogenic bacteria have emerged. One of the methods is the use of nanoparticles such as titanium oxide, magnesium oxide, zinc oxide, nanosilver, and carbon nanotubes (Hossain et al., 2014).

Another emerging water decontamination method is photodynamic antimicrobial chemotherapy (PACT) Photodynamic Antimicrobial Chemotherapy Wainwright (1998) describes PACT as the inactivation of pathogenic microorganisms using a combination of light and a photosensitizer dye. PACT is known to be efficient against multi-antibiotic-resistant strains of bacteria and also a low mutagenic response from bacteria (Jori et al., 2006). Studies have shown that its application can be extended to the inactivation of pathogens in water (Carvalho, 2009). The photosensitizer dye alone is known to have a negligible antibacterial effect. It needs to be activated with light.

The photosensitizer dye absorbs light of the required wavelength and moves from singlet ground state to the short-lived singlet excited state. It then undergoes intersystem crossing to the long-lived triplet excited state where two types of chemical reactions then occur. Type one involves electron transfer reactions between a substrate and the excited photosensitizer. Radicals are produced as a result of this reaction. Radicals can then transfer an electron to molecular oxygen producing superoxide species. Type two reaction involves the transfer of excess energy from the excited photosensitizer to ground state molecular oxygen (3O2). Excited singlet oxygen (1O2) is produced while the photosensitizer’s ground state is regenerated. Reactive oxygen species ROS include singlet oxygen (1O2), superoxide, hydroxyl radical, and peroxyl radicals are molecules with high positive redox potentials. They are known to be very reactive and can destroy biomolecules such as lipids, amino acids, and nucleic acids (Vatansever et al., 2013).

The hydroxyl radical and the singlet oxygen are the most reactive. The superoxide and peroxy radicals being less reactive can be detoxified by cellular endogenous antioxidants induced by oxidative stress (Vatansever et al., 2013). Singlet oxygen reacts with unsaturated carbon-carbon bonds and with conjugated diene systems forming hydroperoxides and endoperoxides and also with guanine bases of nucleic acids (Glaeser et al., 2011). Singlet oxygen is therefore responsible for microorganism’s DNA damage and also to the damage of cytoplasmic membrane, allowing leakage of cellular contents (Hamblin & Hasan, 2004).

Photosensitizers are known to be organic aromatic molecules that absorb photons and cause a change in other molecules/substrates in the system (Donnelly et al., 2008). They are not consumed during the photosensitization reaction but they return to their original form once the photosensitization reaction is complete however studies have shown that they can also be photobleached (Rotomskis et al., 1997). Photobleaching involves a decrease in the absorption intensity of the photosensitizer and is important in ensuring they do not accumulate in the environment. According to O’Connor et al (2009), the ideal photosensitizer used for photodynamic therapy should have certain characteristics that include:

1. They should be non-toxic
2. They should have high singlet oxygen quantum yields
3. They should accumulate sufficiently within the target cells
4. Optimal absorption of visible light

Studies have shown the following dyes to be efficient photosensitizers used in PACT, phthalocyanines, porphyrins, methylene blue, toluidine blue, chlorins and bacteriochlorins (Donnelly et al., 2008). Porphyrins Porphyrins are known to be organic macrocyclic compounds made up of four pyrrole units connected by methine bridges. The 22π electron system gives rise to their long wavelength absorption of light. It is known that the strong conjugation gives porphyrins stability and unique photophysical properties. The nitrogen atoms in the interior of porphyrins can incorporate metal atoms in a tetradentate fashion forming metal complexes. Modification of the porphyrin structure is possible since substituents can be linked to the meso positions at the methine bridges or attached at the pyrrolic β sites. It has been shown that cationic porphyrin photosensitizers are effective in inactivating both gram (-) and gram (+) bacteria as opposed to anionic or neutral porphyrin photosensitizers that are only effective against gram (+) bacteria (Managa et al., 2015).

Anionic photosensitizers are known to be effective against gram (-) bacteria only in the presence of cell membrane disrupting agents such as ethylenediaminetetraacetic acid (EDTA). Synthesis of porphyrins Porphyrin is known to be synthesized by condensation reaction of pyrrole and an aldehyde. There are several methods of substituted porphyrin synthesis with each having different yields and reaction conditions. Adler and Longo Porphyrin synthesis The method is based on refluxing an aldehyde and pyrrole in propanoic acid for 30 minutes. High temperatures of approximately 140 are needed. The porphyrinogen intermediate formed is then oxidized to porphyrin by oxygen in the air. Lindsey synthesis of porphyrins Porphyrins can also be synthesized by the condensation of an aldehyde and pyrrole under argon using a chlorinated solvent such as chloroform or dichloromethane. The catalyst used is a Lewis acid such as trifluoroacetic acid. The porphyrinogen intermediate formed is then oxidized to porphyrin by addition of an oxidant such as tetrachloro-1,4-benzoquinone. After the addition of the oxidant, refluxing for one hour is needed to yield approximately 40%.