Health risk of cyanotoxins in Lake Victoria and household drinking water for riparian communities along Nyanza Gulf

Cyanotoxins are produced by cyanobacteria which are single-celled algae that thrive in warm and nutrient rich water bodies including lakes. There are different kinds of cyanotoxins and microcystin is the most common. Microcystin mostly affects the liver. Epidemiological studies in China and Serbia have shown an association between cyanotoxins and occurrence of Primary Liver Cancer. Cyanobacteria have been reported in Lake Victoria, which is an important source of drinking water for the riparian communities, thus posing a danger to human health. However, the health risk from exposure to toxic cyanobacteria in the Nyanza Gulf water remains unknown. The purpose of this study was to assess the health risk of toxic cyanobacteria to the riparian communities in the Nyanza Gulf. In a longitudinal study adopting survey and experimental design, 127 samples were collected monthly from both households and six beaches over six months. Cyanobacterial levels were determined using an enzyme assay method (PP2A). Different methods of household water treatment were compared. Two-way ANOVA was done to determine statistical significance of microcystins levels. 84% of water samples contained microcystins. Concentration of microcystins was 3.44g/L which is over the WHO limit of 1g/L. There was no variation between beaches and water treatment (ANOVA: F=0.97, p=0.47). Filtration proved to be the most efficient method of water treatment. The health risk factor of cyanotoxins in drinking water is 3.86. There is a health risk posed by cyanotoxins to the residents of the Nyanza Gulf who use the lake water for drinking since is over the WHO limit. This information provides an insight into the quality of Lake Victoria water for drinking. The study recommends development of cyanobacteria removal methods as well as sensitizing the riparian communities on the health risk of cyanotoxins in drinking water.


Introduction
Cyanotoxins from cyanobacteria can cause serious threats to drinking water supplies using surface water as source (Li et al., 2017). Lake Victoria has experienced major deterioration in its water quality mainly due to pollution and Nyanza Gulf is one of the bays of Lake Victoria that is most affected by nutrient enrichment (Gikuma-Njuru et al. 2013). It is estimated that only about 20% of the Kenyan rural population has access to safe water but for both Nyanza and Western provinces, it is only 8% (LBDA, 2004). Drinking water sources are unique and need to be investigated to determine the risk and the best management strategy for cyanotoxins risk reduction.
Different drinking water treatment technologies are applied in different countries and contexts.
Studies investigating cyanotoxins in drinking water and their removal during the water treatment have been even scarcer on the entire African continent (Addico et al., 2017). Cyanotoxins are highly stable in water and are resistant to boiling thus presenting a risk to consumers in less developed regions who collect water from surface sources to drink (Dietrich & Hoeger, 2005).
Based on their toxin production, to which human can be exposed via different routes, the World Health Organization (WHO) has listed cyanobacteria among the emerging health issues (Manganelli et al.,2012). WHO has set the Tolerable Daily Intake (TDI) of microcystin-LR (MC LR) to be 0.04µg/kg-bw/day. For drinking water, the levels of MC-LR should not exceed 1µg/L.
The most cell characterized case on the effects of cyanotoxins in water was the poisoning of renal dialysis patients in a clinic in Caruaru, Brazil, in 1996, where the patients treated in a dialysis clinic during one week suffered severe illness following perfusion, with hepatic failure and death in more than 50 cases. Investigation of the water treatment unit at the clinic found contamination of the filters by two types of cyanobacterial toxin, cylindrospermopsin and microcystins (Jochimsen et al., 1998;Carmichael, 2001). Ueno et al. (1996) hypothesized that the high incidence of Primary Liver Cancer (PLC) in south east China is likely related to microcystin contamination in drinking water.
Another study carried out in Brazil identified microcystin in the serum of highly exposed fishermen in addition to indication of liver damage (Chen et al., 2009). The symptoms of poisoning by the main toxic cyanobacteria in drinking water reservoirs overlap with a range of other gastrointestinal illnesses, largely caused by infectious disease organisms. As a result, during an outbreak of enteric disease, the pathogens are investigated first, as the most probable cause, and only after exhaustive exploration are toxins of any type evaluated.
Agricultural chemicals and industrial pollutants such as heavy metals are likely to be next suspected, with cyanobacterial toxins ignored until well after the event (Teixeira et.al.,1993).
Microcystins require additional attention not only for their ability to cause acute poisoning but also for their ability to initiate cancer through acute doses and potentially promote it through chronic exposure to low microcystin concentrations in drinking water (Lun et al., 2002;Svirčev et al., 2009).
Despite the presence of cyanobacteria blooms in the Lake Victoria water, the health risk this could pose from cyanotoxins has not been assessed. As such, the current study evaluated the health risk of cyanotoxins in both Lake Victoria water and household drinking water for Nyanza Gulf residents. This study established the concentration of cyanotoxins in both Lake Victoria water and household drinking water for Nyanza Gulf. It also assessed the effectiveness of different treatment methods in removal of cyanotoxins. The risk cyanotoxins may be potentially posing to users of the Lake Victoria water was determined. This was done against the TDI and the provisional guideline value set by the WHO.

Study Area
Nyanza Gulf is in Western Kenya whose watershed lies between 0.25N -1.00S latitudes and 34.0E -36.0E longitudes. It covers an approximate total drainage area of 12,300 km2. It has an area of 1400 km2, mean depth 7 m, maximum depth 30 m and a 550 km shoreline that is located entirely in Kenya on the northeast of Lake Victoria (Misigo & Suzuki, 2018).

Sample collection and Analysis
This study adopted both survey research and experimental methods. Survey research approach was used to collect water source, treatment and consumption data at the household level using a structured questionnaire. Experimental methods were used for determination of levels of Microcystins in both lake and household drinking waters. The sample size was calculated using the formula by Fisher's et al. (1998) arriving at 422 subjects. The primary caregiver from each household was selected for participation in the study from the systematically sampled households.
Water samples for analysis of microcystins in the Lake Victoria water were collected once a month for a period of 6 months beginning May to October 2015 from the exact point where the riparian communities draw water from Lake Victoria. Standard water abstraction techniques were used to obtain water in a manner that minimized contamination during sampling. A similar amount of water was also collected from 30% (approx. 127) of all the households sampled.

PP2A
The water samples were analyzed for presence of microcystin using Protein Phosphatase 2A (PP2A) enzyme assay method according to Heresztyn and Nicholson (2001). 2ml of water samples was boiled for an hour then centrifuged for 15 minutes at 3000rpm. 10µl of the supernatant was transferred to a 96-well microplate.  Tolerable Daily Intake of 0.044µg/kg-bw/day (WHO, 1999) Standard Body Weight taken to be 60kg (Falconer & Humpage, 2005) Water Ingested is the average daily water intake in litres by an individual.

Concentration of microcystin in beach and household water
Out of the 127 samples collected from households, 103 (80%) samples were positive for presence of microcystin. For a similar number of samples from the beaches on the lake, 112 (88%) samples had microcystin. On average, 215 (84%) of samples contained microcystin. The highest microcystin concentration was 13.813µg/L and 12.302 µg/L for lake and household respectively while lowest value was 0.151 µg/L for lake and 0.009 µg/L for household. There was a general trend in the level of microcystin in households being lower those of the respective beaches as the

Effectiveness of the various water treatment methods on the level of MC in the households
Water treatment was undertaken in 324 (77%) of the homes not done in the remaining 97 (23%) homes. Out of those that treat their water, 265 (82%) did chlorination which was the most commonly used method of water treatment followed by filtration 20 (6%), boiling 20 (6%), combination of boiling and filtration with 18 (5.6%) and others was 1 (0.5%) as shown in the All 421 (100%) use the lake water for cooking. A higher portion of them, 408 (97%) respondents said use the beach water for drinking including preparation of tea/coffee/porridge while 13 (3%) replied that they don't consume water from the lake in beverages. From the questionnaire responses, it was established that the respondents consumed 6 cups of beach water daily on average either directly through drinking the water or indirectly in tea and food. For this study, the cup of reference had a capacity of 500 milliliters (ml).
In trying to find out the efficacy of the water treatment methods conducted in households, levels of microcystin were recorded at both the beaches and the households.  To find out whether the source of the water (beaches) and the method of water treatment had an effect on the levels of microcystin in the samples drawn from the households, a two-way ANOVA was done. It was found that there was no interaction between the effect of beaches and effect of water treatment method used on the level of microcystin in 127 samples drawn from the households, F(9, 110) = 0.97, P>0.05(P=0.4708). Therefore there was no significant variation in the level of cyanotoxins from samples drawn from household drinking water with regards to treatment method used and the beach from which the water in the household was drawn.

Health Risk based on TDI
The health risk was calculated based on the formula stated earlier. Daily intake of microcystin was calculated and compared with the Tolerable Daily Intake by WHO set at 0.044µg/kg. The risk factor for Ogal beach was the highest at 9.32, followed by Mawembe beach at 7.05. Alum beach had a relatively low risk factor of 1.36 but Rang'ombe was much higher at 3.18. Olambwe beach had a risk factor of 1.59 whereas Kolunga beach had the lowest value at 0.45. On average, the waters of Nyanza Gulf were 3.86 times higher than the recommended TDI.

Discussion
The Tolerable Daily Intake (TDI) is the amount of a potentially harmful substance that can be consumed daily over a lifetime with negligible risk of adverse health effects. This study found that the daily intake of microcystins in the Nyanza Gulf is way above the recommended for drinking water by WHO. The average TDI was four times higher and the average risk factor was four. High levels of risk to human health are linked to the ingestion of large cyanotoxin quantities from water or the intake of small doses during extended chronic exposure (Svirčev et al.,2010).
Therefore, observing that this study found the levels of cyanotoxins in household drinking water way above what is recommended (2.75µg/L), this is posing a health risk to the consumers. Given that this study only focused on drinking water, the daily intake of microcystins could be higher if other sources of microcystin exposure are factored in. For example, in a study conducted by Soares et al. (2004), microcystins accumulate in the liver, muscle and tissues of tilapia and can be subsequently passed to consumers. If these two sources of ingestion of water are combined, especially given that tilapia is a common delicacy in the Nyanza Gulf, it is very likely that microcystins are consumed way more than the TDI recommended in the Nyanza Gulf.
Chronic exposures to cyanobacteria and their toxins have been associated with increased occurrence of liver and colorectal cancer (Yu, 1995;Zhou et al., 2002;Svircev et al., 2009). This is a potential health risk the consumers of the lake water are exposed to due to the levels of cyanotoxins recorded from the samples. According to a survey conducted on the microcystin exposure risk from lakes in Uganda by Poste et al. in 2011, it was shown that more than 50% of the WHO lifetime tolerable daily intake results from consuming untreated drinking water. They recommended strategies of dealing with microcystins from the lake water used for drinking to involve regular monitoring of cell numbers of toxic cyanobacteria in the raw water. Such methods include removal of particles by flocculation and ozonation followed by activated carbon filtration or sand filtration to remove dissolved microcystins (Chorus & Bartam, 1999).
None of these methods is currently in the households sampled during the study, for treatment of drinking water. Chlorination which is the most commonly used method for treating drinking water in the households sampled is not very effective in destroying cyanobacteria and cyanotoxins.
Although there was a decrease in cyanobacteria concentrations in households where chlorination was used to treat water, the difference is not significant. The efficiency of chlorination depends mainly on the chloride compounds used as well as the concentration used. Filtration is comparatively more effective in removing cyanobacterial cells but dissolves toxins remain in the drinking water.
Cyanotoxins occur in two modifications: cell bound and dissolved in water. This study therefore identified a need for water treatment methods for removal of cyanotoxins. Given that a population of 94 000 inhabitants of the Nyanza Gulf depend on the lake water for drinking, development of methods that will remove cyanobacterial cells as well as get rid of cyanotoxins in the water is paramount. Although adverse health effects have not been documented from the region, we cannot rule out any effects of drinking water contaminated by cyanotoxins. In other countries such as China and Serbia (Svirčev et al., 2010;Svirčev et al.,2009;Svirčev et al., 2007;Ueno et al., 1996) where cyanobacteria and cyanotoxins occurrence in water is much studied and effects documented, chronic exposure to cyanotoxins has led to liver and neurological diseases.

Conclusion and Recommendation
There is a health risk posed by cyanotoxins to the residents of the Nyanza gulf who use the lake water for drinking since the microcystin levels for drinking water is four times the TDI that is recommended by WHO and the risk factor is four. Ways of getting rid of the cyanotoxins identified need to be developed. This should include the removal of both intracellular and extracellular toxins. There should be sensitization of the riparian communities about the health risk that comes with consuming water contaminated with cyanobacteria and cyanotoxins. The county governments should carry out advocacy sessions in the riparian communities regarding the health risk of cyanotoxins from drinking water directly from the lake.