A three-month investigation, Rotting from the Deep, can now reveal why Africa’s biggest freshwater lake is dying a slow death that has seen more than a dozen fish species disappear.
We selected 28 sampling points for this study. These locations were identified due to proximity to contamination through waste discharge or levels of human activity.
The sample locations included the mouths of Migori and Kuja rivers, Homa Bay, River Awach, Kendu Bay, Sondu River, Dunga Beach, Kisat River at the golf club, Usoma Beach, Nyando River and near Kisumu Resort.
We also collected samples at Marenga Beach, River Saka at Kodiaga Prison, River Nzoia near Panpaper’s effluent discharge point and waste from the jaggery factory at Webuye. Other samples were collected at various factory effluent discharge points including those from Kibos Sugar and Kisumu Water and Sewerage Company (Kiwasco).
We travelled to Uganda and also sampled the Nakivubo channel, which carries waste from Kampala into Lake Victoria. We picked more samples at Gabba area near Kampala, at Masese Beach and in Jinja at the source of the Nile. On the lake, we sampled various places, including the lake deep, lake surface and near the shores.
From all these locations, we collected a total of 54 samples of water, fish and sediments.
Our study showed that the contamination is spreading from the shores heading towards the middle of the lake.
Among the poisons, we found at least eight metals in various concentrations, with the most toxic being 75 times more poisonous than recommended levels.
The metals found in most of the sampling points include lead, mercury, cadmium, chromium, zinc, iron, manganese and fluoride.
Lead was widely distributed, especially in Migori, Kendu Bay, effluent flowing through Nyanza Golf Club, Kodiaga Prison discharge point, Nyando River, Jinja waters, and fish from Masese Beach in Uganda and Marenga Beach in Kenya.
The metal causes decreased mental, nervous system and physical development in children. In adults, it causes high blood pressure, kidney damage and reduced fertility. We also found lead in excessive quantities in the fish imported from China that was being sold in Kisumu City and adjacent towns.
Out of the 28 sampling points comprising the lake and its catchment rivers as well as discharge points and the Nile, River Awach had the highest number (67 per cent) of heavy metals detected at levels above the recommended KS levels. The metals were mercury, lead, cadmium, chromium, iron and manganese.
The second most contaminated was River Kisat that was sampled at the Nyanza Golf Club, with five out of nine (56 per cent) heavy metals including mercury, lead, cadmium, chromium and iron.
This level of contamination could be attributed to, among others, the effluent discharged to the river from the KIWASCO treatment site.
River Migori, at its mouth as well as the discharge point at Kendu Bay, had four out of nine (44 per cent) of the heavy metals detected above the recommended levels. These were mercury, lead, cadmium and chromium.
Mercury detected at River Migori could be as a result of the gold mines that discharge waste into the river.
“Observations made during sample collection showed a lot of negligence in handling of mercury by the gold miners as they use it to process gold. High level of self-exposure with the toxic chemical and its vapour, as well as environmental and water contamination, is rampart in this area,” the research report reads.
We also found DDT (Dichlorodiphenyltrichloroethane), a banned pesticide that has adverse effects on humans and aquatic animals."
The discharges at Homa Bay and Kisumu Beach had the least number of heavy metals, including cadmium and lead at one out of nine (11 per cent) metals detected above KS recommendations.
In all the water samples tested in the first phase of sampling, cadmium was found in 18 out of 20 (90 per cent) samples at above recommended levels, second was lead at 13 out of 20 (65 per cent), then chromium 11 out of 20 (55 per cent), while mercury and manganese were at four out of 20 (20 per cent).
In the second phase of sampling, all the five water samples had more than 44 per cent heavy metals contamination, the lowest being from the Nile at Jinja.
Seven metals were shown to be occurring at levels above the Kenya recommended levels for drinking water in more than 60 per cent of the samples. These were lead, copper, chromium, zinc, iron, manganese and fluoride.
We also found DDT (Dichlorodiphenyltrichloroethane), a banned pesticide that has adverse effects on humans and aquatic animals. Other pesticides we detected include endosulfan and mirex. These pesticides can cause cancer, mouth ulceration, dysphagia and abdominal pain, among other diseases, if ingested. DDT was banned as a pesticide worldwide under the Stockholm Convention in 2001 after it was discovered to be dangerous to wildlife and the environment.
Pesticides are unlikely to occur in drinking water, according to WHO guidelines. There are therefore no recommended residue levels available for most of them.
In this study, up to 21 different pesticides, including organochlorines, organophosphates and pyrethroids were detected at different concentrations and frequencies in the water samples.
The WHO pesticide evaluation scheme (Whopes) programme approves pesticides for direct application to drinking water for control of insect vectors transmitting disease.
Guideline values are therefore available for a few pesticides as maximum levels in drinking water namely: chlorpyrifos (0.03ppm), DDT and its metabolites (0.001ppm), permethrin (0.30ppm) and pyriproxyfen (0.30ppm). Amongst these, only pyriproxyfen has been approved by WHO for addition to water for public heath purposes.
Some of the pesticides found in the samples analysed from the Lake Victoria and its catchment rivers are of known toxicity to both humans and aquatic life.
The pesticides found include fenitrothion, an organophosphate used as insecticide and which is toxic to aquatic life; chlorofenvinphos, which affects the respiratory system in humans; cyhalothrin, which has been shown to cause irritation of the mucous membrane; and bifenthrin, which is very harmful to aquatic life and has been classified as a possible human carcinogen.
A few of the pesticides in the water have been globally banned due to their toxicity and environmental persistence. These include DDT, which is highly persistent in the environment, very soluble in water, affects reproduction in humans and has been classified as a possible human carcinogen.
Endosulfan, which was globally banned in 2012, is an insecticide and a known neurotoxic, causes birth defects, and has the ability to bio-accumulate.
Another banned pesticide detected was mirex, which is also a bio-accumulator and persists in the environment as an organic pollutant thus affecting aquatic life. It’s a carcinogenic and an endocrine disruptor.
In the first phase, River Kodiaga was found to have the highest number of detectable pesticides with 10 out of 21 (48 per cent), these are benfluralin, linuron, chlorofenvinphos, cyhalothrin, azinphos, oxyfluoren, methoxychlor, DDT, DDE and endosulfan. DDT was detected at 3.49 ppm, which was the most concentrated pesticide detected in water in this study.