In many countries, the biggest source of water pollution today is agriculture, not cities or industry, while world-wide, the most common chemical contaminant found in groundwater aquifers is nitrate from farming, according to More People, More Food, Worse Water? A Global Review of Water Pollution from Agriculture. This new report was launched by the UN Food and Agriculture Organization (FAO) and the International Water Management Institute (IWMI) at a conference in Tajikistan in June 2018.
Modern agriculture is responsible for the discharge of large quantities of agrochemicals, organic matter, sediments and saline trading into water bodies, the report says.
The agro-pollutants of greatest concern for human health are pathogens from livestock, pesticides, nitrates in groundwater, trace metallic elements and emerging pollutants, including antibiotics and antibiotic-resistant genes excreted by livestock.
The boom in global agricultural productivity that followed the Second World War was achieved largely through the intensive use of inputs such as pesticides and chemical fertilisers.
Since 1960 the use of mineral fertiliser has grown tenfold, while since 1970, global sales of pesticides climbed from around USD one billion to USD 35 billion a year.
Meanwhile, the intensification of livestock production — world livestock numbers have more than tripled since 1970 — has seen a new class of pollutants emerge: antibiotics, vaccines and hormonal growth promoters that travel from farms through water into ecosystems and our drinking water.
At the same time, water pollution by organic matter from livestock farming is now significantly more widespread than organic pollution from urban areas.
And another booming sector, aquaculture (which has expanded twenty-fold since 1980) is now releasing ever greater amounts of fish excreta, uneaten feed, antibiotics, fungicides and anti-fouling agents into surface waters.
The most effective way to mitigate pressure on aquatic ecosystems and rural ecologies is to limit the export of pollutants at the source or to intercept them before they reach vulnerable ecosystems. Once off-farm, the costs of remediation progressively increase.
One way to do this is to develop policies and incentives that encourage people to adopt more sustainable diets and limit increases in demand for food with a large environmental footprint — for example by introducing taxes and subsidies.
"Traditional" regulatory instruments will also continue to be a key tool in reducing farm outputs of pollutants. These include water quality standards, pollution discharge permits, mandatory best practices, environmental impact assessments for certain farming activities, buffer zones around farms, restrictions on agricultural practices or the location of farms, and limits on the marketing and sale of dangerous products.
However, the report acknowledges that well-known principles for reducing pollution, such as ”polluter pays”, are hard to apply to non-point agricultural pollution because identifying the actual polluters is neither easy nor cheap.
That means that measures that promote farmer "buy in" are critical to preening pollution at the source — such as tax breaks for the adoption of practices that minimise farm export of nutrients and pesticides or payments to farmers for "landscape maintenance”.
On the farm, a number of best practices can reduce the export of pollutants into surrounding ecosystems, such as minimising the use of fertilisers and pesticides, establishing buffer zones along watercourses and farm boundaries, or improving drainage control schemes.
Integrated pest management, which combines the strategic use of pest-resistant crop varieties with crop rotation and the introduction of natural predators of common pests is another helpful tool.
Facts and figures of agricultural pollution
• On livestock operations, traditional techniques such as restoring degraded pasturelands and better managing animal diets, feed additives and medicines are needed — while more also needs to be done with new nutrient recycling techniques and technologies, such as farm waste bio digesters.
• Irrigation is the world's largest producer in volume of wastewater (in the form of agricultural drainage).
• Globally, around 115 million tonnes of mineral nitrogen fertilisers are applied to croplands each year. Around 20 per cent of these nitrogen inputs ends up accumulating in soils and biomass, whereas 35 per cent enters the oceans.
• World-wide, 4.6 million tonnes of chemical pesticides are sprayed into the environment each year.
• Developing countries account for 25 per cent of world pesticide use in farming, but 99 per cent of the world's deaths due to pesticides.
• Recent estimates that the economic impact of pesticides on non-target species (including humans) is approximately USD 8 billion annually in developing countries.
• Oxygen depletion (hypoxia) resulting from anthropogenic nutrient overloading affects an area of 240,000 km2 globally, comprising 70,000 km2 of inland waters and 170,000 km2 of coastal areas.
• World-wide, an estimated 24 per cent of the area under irrigation is affected by salinisation.
• Currently, more than 700 emerging pollutants, their metabolites and transformation products, are listed as being present in the European aquatic environment.