INTRODUCTION:

Cyanobacterial toxins are the naturally produced poisons stored in the cells of certain species of cyanobacteria.¹ Very few cyanobacterial toxins have actually been isolated and characterized to date. One group of toxins produced and released by cyanobacteria are called microcystins because they were isolated from a cyanobacterium called Microcystis aeruginosa.

Microcystins are the most common of the cyanobacterial toxins found in water, as well as being the ones most often responsible for poisoning animals and humans who come into contact with toxic blooms.¹ Microcystins are extremely stable in water because of their chemical structure, which means they can survive in both warm and cold water and can tolerate radical changes in water chemistry, including pH. So far, scientists have found about 50 different kinds of microcystins. One of them, microcystin-LR, appears to be one of the microcystins most commonly identified in water supplies around the world. For this reason, most research in this area has focused on this particular toxin.

Microcystins have been described and detected in several cyanobacteria genera. These include Anabaena, Microcystis Oscillatoria, Planktothrix.^2-5 Worldwide, the nearly all cyanotoxin encountered in fresh and brackish waters are the cyclic peptides known as microcystin.⁶

Cyanobacteria toxins fall into various categories. Some are known to attack the liver (hepatotoxins) or the nervous system (neurotoxins); others simply irritate the skin. People swimming in dense Microcystis blooms have experienced irritation such as skin rashes, burns, and blistering of the mouth. Ingestion or inhalation of water containing dense bloom material may cause vomiting, nausea, headaches, diarrhea, pneumonia, and fever. Ingestion of significant levels of the toxin microcystin can cause liver damage and dysfunction in humans and animals.

Microcystins have been described as potent liver toxins⁷, and in chronic cases are known to promote or initiate the growth of tumours. In other cases, they have been found to inhibit protein phosphatase activity.⁸ They are synthesized non-ribosomally and by thiotemplate mechanisms. In Kenya, there have been few studies on cyanobacteria, cyanotoxins and possible adverse public health effects on humans. This is despite the established knowledge that cyanobacteria have been implicated in several poisoning episodes of humans and animals worldwide through drinking water.

In Bahia, Brazil, Anabaena and Microcystis (cyanobacterial toxins) from drinking water resulted in the death of 88 children from over 2000 cases of gastro-enteritis over a period of 42 days.⁹ Another case of human mortality occurred in Brazil, at a haemodialysis clinic where patients were treated with drinking water contaminated with cyanotoxins.¹⁰ Over 50 people died in this incident. Examination of the phytoplankton in the reservoir showed the dominance of the cyanobacteria Microcystis, Anabaena and Anabaenopsis. A more recent scenario is the poisoning of domestic water supply system in Toledo (Ohio), USA. Consequently, water supply to the city had to be suspended for weeks in order for authorities to ascertain the commodity’s safety before restoring supply. In this paper, we report the presence of microcystins in Lake Naivasha.

MATERIALS AND METHODOLOGY:

All reagents used in the study were of analytical grade. The reagents were purchased from commercial suppliers and used directly without further purification. The samples were collected from Lake Naivasha (Nakuru County, Kenya) and filtered through cartridge within four hours of collection for analysis. Solid phase extraction cartridges, Sep-pak© light tc18, were obtained from Waters Corporation Milford, Massachusetts USA. The Brannan 76 mm pH meter (UK) and UV-Vis (1800 240V Shimadzu) were used in analysis of samples, in addition to HPLC and computation techniques.

In order to analyze the concentration of microcystin, water samples were concentrated according to the literature procedure.¹¹ Preliminary studies of microcystins were carried out using UV spectra (200-300 nm) and confirmed using HPLC-PDA retention times reported in literature.

RESULTS AND DISCUSSION:

The physico-chemical properties of the water samples were analyzed and the results are recorded in Table 1. The colour of the water samples ranged between 520 ± 91 ptco, signaling low transparency throughout the period. The conductivity was 234 ± 0.8 µs/cm and the total dissolved solids were found to be 1035 ± 12 mg/L. The pH of the lake remained slightly alkaline, averaging about 7.6 for the period under study. Due to the high turbidity (59.0 ± 24 ntu), phytoplankton biomass was low, ranging between 1.5 and 8.2 mg L^-1.

Table 1: Physico-chemical properties of Lake Naivasha

Parameter	Jan	Feb	March
Water temperature (°C)	26.1	26.3	26.7
pH	7.41	7.88	7.62
Turbidity (ntu)	69.0	59.4	44.6
TDS	1035	1054	1025
Colour (ptco)	377	306	360
Conductivity (µs/cm)	235	236	234

Using UV-Vis and HPLC techniques, the microcystin-LR and -RR were detected in all the water samples collected from the lake. Microcystin-LR, and microcystin-RR were identified based on their retention times, 11.45 and 5.01 respectively as shown in Figure 1.¹²

Fig. 1. HPLC-PDA chromatogram of water from Lake Naivasha.

Log P value, which is usually calculated as the octanol-water partion coefficient, is a measure of the toxicity index of a molecule. In this case, microcystin-RR is approximately 230 times more soluble in water than in octanol (Table 2). Thus, microcystin-RR (Figures 2A and 2B) is highly hydrophilic and may react with polar biological tissues, causing extensive cell injury, oxidative stress, and ultimately cancer. Lipophilicity, as measured by the base 10 logarithm of the octanol-water partition coefficient (P) and denoted as log P, is included as a possible contributory factor to the toxicity. Log P correlates with a number of biological activities including in vitro mutagenicity and carcinogenicity.¹² Lipophilic compounds including microcystins can cross biological barriers which contain lipids, for example, cell or microsomal membranes and skin stratum.^13,14 Therefore, log P influences metabolic fate, intrinsic biological activity and the biological transport properties of chemicals.¹⁴

Table 2. Molecular properties of microcystin-RR

Name	Log P	P	Molar mass (a.m.u)
Microcystin-RR	-2.36	0.004	1024.19

Fig. 2A: Molecular structure of microcystin-RR

Fig. 2B: The modeled structure of microcystin-RR

Our study revealed that cyanobacteria in Lake Naivasha produce microcystins. Microcystin-LR and microcystin-RR were found in varying amounts. Worldwide, more than 60 structural variants of microcystins have been isolated.^9,15 Estimated as microcystin concentration per litre of lake water, the concentrations of microcystins-LR equivalents in Lake Naivasha range from 0.06 to 1.3 μg MC equ L^-1 lake water. These values are within the safe level of Health Canada of 1.5 μg MC equ L^-1.^9,16 Although the levels are acceptable, the situation may change especially after Kenya changed its status from low-income economy to middle-income economy. There is expected to be accelerated use of fertilizers within Naivasha area in order to feed its rising population and this may lead to growth of algal blooms. This will raise the concentrations to levels that can have serious ecological impact on aquatic food web of the lake and cause serious health problems.^15,17,18

CONCLUSION:

The impact of microcystins on the food web of Lake Naivasha, domestic animals and on public health in the region has so far not been investigated. The lake water is used by locals as drinking water for households and domestic animals. In some cases, the water is either used without treatment or treated with aluminium sulphate to settle down the sediments. To minimize harmful effects on consumers, we recommend that the water of Lake Naivasha should be pretreated in order to remove the any cyanobacterial toxins that may pose health hazard to the consumers. Further research also needs to be carried out in order to provide an up to date data on microcystins at Lake Naivasha and other water bodies in Kenya.

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Received on 30.03.2016 Modified on 10.04.2016

Asian J. Research Chem. 2016; 9(5): 217-220

DOI: 10.5958/0974-4150.2016.00037.7