By Mery Rodrigues, Ecologist
The Infulene River is a body of water that runs from north to south in Maputo province and flows into the Espírito Santo estuary. The river is a natural water source, with an almost permanent flow, and it benefits about 3,000 farmers who occupy 422 hectares of land in its basin. The agricultural production from these fields accounts for 40% of the consumption of Maputo city.
Despite its great importance for agricultural production, the Infulene River is exposed to pollution, including discharges of wastewater from the brewing industry, discharges from the Infulene and Zimpeto wastewater treatment stations, discharges of water from the Maputo drainage system, which collects water from informal settlements with precarious sanitation, and the surface run-off of agricultural and human wastes.
The main production in the Infulene River basin is in the region downstream from the river, in Infulene neighbourhood, a region which, because of its location, receives pollutants from specific and diffuse sources. The main crops grown in the Infulene basin are vegetables such as lettuce, spinach, and cabbage, which are sold in the markets in Maputo and Matola cities.
The type of pollution of the Infulene River depends on the source of pollution. For example, in 2022 the brewing industry emitted a high concentration of indicators of pollution such as Biochemical Oxygen Demand (BOD) with 62mg/L over 30mg/L and of the Escherichia coli bacterium with 2.000.000MPN/100ml over 400/100ml, concentrations higher than those stipulated in Decree 18/2004, of 2 June, which regulates Environmental Quality and Effluent Emission Standards. Domestic and urban discharges show a high concentration of the E. coli bacterium (35.900.000MPN/100ml) and of nutrients such as phosphates (8.39mg/l) and nitrates (22.49mg/l). In the Infulene River basin, the concentrations of these pollutants vary over the year. The highest pollution levels have been found during the rainy season (summer), due to the greater surface run-off which sweeps the pollutants from the surface into the river.
Several studies held on this river show that the specific and diffuse sources mentioned above have damaged the quality of the water used for irrigation. The water of the Infulene River is unfit for swimming and for irrigation (particularly for crops that are eaten raw) because it is murky, with high amounts of total dissolved solids, DBO, phosphates, chlorophyll, and highly contaminated with pathogenic micro-organisms such as parasites and the Escherichia coli bacterium.
The high concentration of BOD indicates that there are high levels of decomposing organic matter in the water, and this is one of the causes for the reduced concentration of oxygen in the water. This oxygen is important for the survival of aquatic aerobic organisms, including fish. The excess of decomposing organic matter favours the massive growth of algae (eutrophication), generally consisting of cyanobacteria with the potential to produce toxins that are damaging to human beings and to other animals.
The use of water from the Infulene River to irrigate vegetables eaten in Maputo and Matola cities is a threat to the public health, both of the producers, due to direct contact with contaminated water, and of the sellers, due to their contact with contaminated vegetables. But those who are exposed to the greatest risk are the consumers, because they have ingested the contaminated vegetables.
Ingesting contaminated water or vegetables could cause serious public health problems in the cities of Maputo and Matola, such as diarrhoea, gastroenteritis, urinary infections, cystitis, hemorrhagic colitis, pneumonia, bacteremia, and abdominal infections such as spontaneous bacterial peritonitis.
Although the Infulene River is a key raw material in the agricultural supply chain, with positive impacts on the economy since it provides income to farmers, market and retail sellers, and generates taxes from this chain of sales, the National Directorate of Water Resource Management and the Maputo and Matola municipal authorities have done little to improve the quality of this precious water source.
The feeble performance of the managers to hold responsible those who pollute the river and to improve the quality of the water, may lead to serious public health problems from handling and consuming contaminated vegetables. It may also affect the income from the sales chain, since the number of consumers of vegetables from the Infulene River could decline because of the fact that farmers are using polluted water to irrigate their fields.
Measures to improve the quality of the water of the Infulene River basin should include i) providing training for farmers and controlling the use of fertilisers, pesticides and agricultural waste; ii) installing waste deposits and public toilets; iii) regular treatment and monitoring of domestic and industrial wastewater; iv) improving the sanitation in informal settlements to reduce the contamination of the drainage waters; v) imposing sanctions and penalties on polluters, and vi) revising Decree nº 18/2004 of 2 June, in the section on the quality standards for the emission of effluents, restricting emission standards for E. coli concentration to 100MPN/100mL, phosphates concentration to 0.03mg/L; nitrates concentration to 5mg/L, and adding quality control of river parameters such as chlorophyll concentration to up to 15µg/L. (MR)
