Introduction
Food security exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.1 Close to 750 million people were exposed to severe levels of food insecurity and an estimated two billion people face some form of food insecurity, i.e. without regular access to safe, nutritious and sufficient food.2 Achieving the Zero Hunger target set by Sustainable Development Goal 2 in the world by 2030 remains a huge challenge.
Water plays an important role in food production, mostly through crop irrigation. But the impact of water quality on food products and industries is often underestimated. Irrigated agriculture accounts for 20 per cent of total cultivated land, and about 40 per cent of crop production worldwide is harvested from irrigated land.3 Crop yields are higher on irrigated land: the same area can be cultivated more than once a year under favourable climate and water conditions.
Salinity is the biggest threat as saline water results in salt accumulation in soil. This increases soil osmotic pressure and so reduces water uptake by crops and inhibits photosynthesis by decreasing CO2 availability to the plant cells, leading to reduction in crop yield and plant nutrition.4
Globally, about 70 per cent of abstracted water is used by agriculture, mainly for irrigation, and including livestock and aquaculture.5 Based on FAO AQUASTAT country statistics, globally 34 million ha (ca. 11 per cent) of irrigated land is salinized by irrigation to some degree, and an additional 60-80 million ha are affected by waterlogging and related salinity. This compromises food productivity, especially in large irrigation schemes in India, Pakistan, China and the United States.
Arsenic in groundwater is another problem worldwide, but is most severe in Southeast Asian countries.6 Arsenic in groundwater used for irrigation is an important source of arsenic accumulation in topsoil, depending on the crops grown.7 However, arsenic also bioaccumulates in vegetables, rice and other crops, which poses a risk for food-chain contamination and human health.8
Aquaculture is an important source of protein in much of the world. Global aquaculture production has increased from fewer than 1 million tonnes (Mt) in 1950 to 110 Mt in 2016, while the growth of capture fisheries production has peaked.9 Although aquaculture contributes to local water-quality deterioration, it is at the same time vulnerable to eutrophication and hypoxia in rivers and coastal waters from anthropogenic nutrient loading.10 Climate effects such as increasing temperature can foster Cyanobacteria and harmful algal blooms in aquaculture ponds.
Food safety is affected by the quality of water used in irrigation, and also by that along the entire supply chain from food production to consumption. Water used in each step of the supply chain can be a source of exposure to various contaminants, such as pathogens, heavy metals, persistent organic pollutants (POPs), emerging pollutants (e.g. Triclosan) and microplastics. Microbial contamination of irrigation water is of concern for leafy crops,11 while heavy metals, POPs and microplastics tend to bioaccumulate in aquaculture,12 livestock13 and soils.14
Food security and safety cannot be achieved without tackling water issues, since lack of safe water worsens food insecurity. Polluted irrigation water damages health and nutrition and reduces food production, constraining agricultural and economic development, especially in densely populated regions where water is already scarce and wastewater treatment is poor. It is difficult to quantify the impact of water quality on food security because the necessary data are often lacking. Data derived from water-quality modelling in combination with remote sensing can close data gaps and so help to identify hotspots and map the pathways of pollutant intakes.
Salinity pollution
Impact and state
About 34 million hectares of irrigated land worldwide (equalling 340,000 km²) are affected by salinization (ca. 11 per cent of the global irrigated area), 77 per cent of which is in Asia, particularly in Pakistan, China and India. Using saline water for irrigating crops can result in severe yield losses and decreased quality.15 In South Asia, the total irrigated area has increased by about 8 per cent in 2008-2017. The non-rice irrigated area increased 12 per cent in the same period. These areas are mainly in India and Pakistan, constituting about 70 per cent and 12 per cent of the total irrigated area respectively. Severe salinity concentrations (exceeding 450 mg/l, according to FAO guidelines) in surface water likely impair the use of river water for irrigation. Likewise, the threatened irrigated area has steadily increased, driven by the growing trend in surface water irrigated area. Model outcomes reveal that more than 200,000 km² (22 per cent of the irrigated area) of agricultural land may be irrigated with saline water exceeding 450 mg/l. Estimates indicate that Afghanistan, Pakistan, Sri Lanka, and India are at higher risk.
A common metric of salinity in rivers is the concentration of total dissolved solids (TDS). Global spatial patterns of simulated salinity in terms of TDS in-stream concentrations show hotspots in north-eastern China, India, the Middle East, parts of South America, Africa, Mexico, the United States and the Mediterranean (Figure 3.17). These simulated hotspots correspond well with salinity hotspots derived from global monitoring data.16 Salinity pollution especially threatens areas where surface water with relatively low dilution capacity is in high demand for irrigation. This poses a considerable risk for food security in semi-arid regions.
Upstream land use affects the quality of water entering the irrigated area downstream and reduces water availability and quality for irrigation (Figure 3.18). South Asia is one of the hotspots where water quality degradation because of high salinity impacts agricultural food production.
Drivers and pressures
Two main causes of salinization influence food production: primary salinization where soluble salts accumulate in soils through natural processes, and secondary salinization as a result of anthropogenic interventions such as return flow from irrigation, wastewater treatment, industrial and mining operations, road de-icing and overextraction of groundwater aquifers. Irrigation water use plays a key role in hotspot regions. Strong interactions exist between salinity and different sectoral water uses.17 There is diversity in contributing sources between regions, with a high contribution of irrigation return flow in Asia and Africa, manufacturing in North America and Europe, and manufacturing and domestic use in South America (Figure 3.19).
Population growth, wealth and dietary changes have increased food production from irrigated land. This drives the expansion of irrigated area and intensification of land-use and management practices and hence contributes to an increase in salt-affected area (Figure 3.20). In addition, climate change accelerates both primary and secondary salinization through higher temperatures, less rain, and reverse evaporation rates, which in turn affect irrigation requirements.18
Figure 3.20 Salt affected land area for different years Ivushkin et al. 2019).
Arsenic pollution
Impact and state
Next to salinity impacts, high levels of arsenic in groundwater are a risk for irrigation in South Asia, too. Health impacts of consuming arsenic in such crops are varied and are generally the result of long-term ingestion, causing arsenicosis (arsenic poisoning).
It is estimated that more than 154,000 km² of agricultural land in South Asia may be irrigated with groundwater that exceeds the WHO guideline value of 10 µg/l. This estimate is based on a global prediction model of the occurrence of naturally occurring arsenic in groundwater (Figure 3.22) as well as maps of areas equipped for irrigation.19 The Kashmir Valley, parts of Punjab, and the states of Haryana and Uttar Pradesh in India are vulnerable because of poor quality ground-water and surface water used in irrigation. These are generally areas characterized by high irrigation intensity (above 60 per cent) and overexploited groundwater resources that, nonetheless, contribute to more than 35 per cent of the total production of food grain in India.20
Drivers and pressures
Arsenic is present in trace amounts throughout the Earth's crust and, as such, often leaches from rocks and sediments into groundwater. In South Asia, anoxic conditions in aquifers often lead to the release of arsenic that is present in geologically recent sediments, particularly along the Indus and Ganges rivers (Figure 3.22). Arsenic release in aquifers is controlled by climate; precipitation and evapotranspiration processes are of particular importance because they create conducive conditions for arsenic release under reducing conditions (e.g. waterlogged soils), as is high aridity associated with oxidizing, high-pH conditions.
Nutrient pollution
Impact and state
A large amount of freshwater fish and shrimp are cultured in ponds.21 Aquaculture in cages, and shellfish (oyster, mussels, abalone) production are sensitive to water pollution and algal blooms. Aquaculture production is located in water bodies seriously affected by phosphorus loading, which, in freshwater, is the major driver of eutrophication. There is a strong overlap between aquaculture production regions and phosphorus loading. For example, freshwater aquaculture production may be at risk in southern and eastern Asia (Figure 3.23). Cyanobacteria, one of the species responsible for harmful algal blooms in freshwater, bloom under conditions of low nitrogen and high phosphorus availability.22 There is a marked difference in ecological functioning between freshwater systems and coastal waters. This is due to multiple factors including N2 fixation in freshwater systems and the lack thereof in coastal systems, and differences in nitrogen and phosphorus recycling between lakes and coastal systems. Common metrics of eutrophication (e.g. chlorophyll-a), total nitrogen, and total phosphorus alone are not adequate for understanding biodiversity changes, especially those associated with harmful algal bloom proliferations. Harmful algae can increase disproportionately with increasing nutrient loading, depending on the proportion in which nutrients are available. Intensive aquaculture production in Eastern and Southern Asia is in sea regions where the river inputs are dominated by anthropogenic nitrogen sources and have high nitrogen-to-phosphorus ratios. Many reports show that Chinese mariculture frequently experiences production loss due to harmful algal blooms.23
Satellite data help to identify areas affected by cyanobacteria, harmful algal blooms, and growth of phytoplankton biomass by, for example, using retrieved chlorophyll-a concentration (Figure 3.25). This study can be extended globally as well as underlined with larger time series data of high-resolution satellite images. Harmful bloom indicators calculated from satellite data can further support the monitoring of aquaculture; datasets are also available in the SDG6 portal (see Table 2.1). In order to identify aquaculture fields that could be at risk from unfavourable water quality conditions, all inland water bodies larger than 0.05 km² have been assessed using satellite data and then classified (after Carlson, 1977) into four main trophic states ranging from oligotrophic to hypereutrophic. In the given Chinese example, the majority, 55 per cent are mesotrophic, which equals a range of 2.6 to 20 µg/l chlorophyll-a.
Drivers and pressures
The anthropogenic impact on river nutrient loading has been increasing rapidly, from about 6 Tg N yr-1 (equals 6 Mio tonnes) in 1970 to 24 Tg yr-1 (24 Mio tonnes) in 2015, which is 43 per cent (56 Mio tonnes) of the total global river nitrogen. This dramatic increase in nutrient loading has not been compensated by increased retention in river basins.24 At present, river basins dominated by anthropogenic sources correspond to densely populated regions, with intensive food and energy production, and population centres where sewers dispose of waste streams from households and industries.
For dissolved inorganic nitrogen, agricultural use of synthetic fertilizers, animal manure, atmospheric nitrogen deposition and fixation are the dominant sources in rivers. This is different for dissolved organic nitrogen and phosphorus as direct manure discharges to rivers are dominant sources of nutrients in rivers in many parts of China. Inadequate sewage systems are major sources of increased nutrient concentrations in urbanized areas and contribute to harmful algae blooms, eutrophication, and low dissolved oxygen and formation of hypoxic or dead zones. Both capture fisheries and aquaculture are vulnerable to external factors that lead to a reduction in water quality.25
Food safety
Water quality is also a concern for food safety, as it might impact the health of ecosystems and humans through the food chain. The fate of chemicals used for agricultural purposes, such as pesticides, is determined by substance properties and by processes such as degradation, sorption and sedimentation in the soil and the aquatic environment. These chemicals could accumulate in different environmental compartments and enter the food chain, causing concern for the environment and human health. Wastewater reuse in irrigation is an option to overcome water shortages and to close the nutrient cycle, but food may become contaminated by pathogens (and faecal coliform bacteria), antimicrobial resistant microorganisms, and chemicals in wastewater that has not been treated sufficiently. In addition, wastewater reuse might bring other negative effects such as soil salinization and bioaccumulation.
Emerging pollutants such as Triclosan, an antibacterial and antifungal chemical used in hygiene products,26 and microplastics are discharged into rivers through sewage systems. In the aquatic environment, Triclosan could pose a risk to various aquatic organisms, for example by acting as an endocrine disruptor,27 whereas marine and riverine fish are affected by microplastic contamination.28 River basins with high Triclosan and microplastics inputs are characterized by high urbanization and mainly located in Europe, India, China and some individual sub-basins in South and North America. These hotspots largely match areas of high nutrient and pathogen loads. Main sources of Triclosan in sewers is the use of personal care products, while of microplastics are laundry, household dust, the use of personal care products and car tyres wearing on roads.
Response options
• Although different arsenic filtration technologies exist, they are generally not capable of handling the large quantities of water used in irrigation.
• Proper irrigation management measures can help to restore the salt balance in the soil profile, which mitigates the negative impacts from irrigation with saline water.
• Mismanaged waste is one of the most important sources of plastic pollution. Responses should be directed to policies to better collect and manage solid waste (e.g. circular economy).
• Reduction of pollution discharge by improved wastewater treatment to decrease pollution intake into freshwater systems and support safe use of wastewater reuse.
• High nutrient use efficiencies and improved manure management (i.e. recycling of manure on land instead of dumping to rivers).
• Stricter and upfront regulatory assessment and restrictions are needed on the use of emerging pollutants (e.g. Triclosan) and microplastics as the most fundamental source control measure to limit contaminants entering the environment and subsequently the food system.
Missing data/more research required
• Models cover some but not all of the important water quality parameters. More research is needed to better understand natural and human-driven processes, environmental behaviour and interaction with food production and food safety.
• The assessment of water-quality impacts on food security is difficult in quantitative terms as in-situ data and modelling data are lacking. For example, the impacts of HABs and hypoxia on capture and aquacultural fisheries and pathogen (or faecal coliforms as a proxy) contamination impacts on leafy crops and food safety.
• More research is needed to understand the effects of response strategies and to demonstrate their efficiencies.
• The application of remote-sensing data and information in regard to water quality is (so far) limited to address water quality challenges. Further exploitation of data and improvements in model accuracy and data resolution are required as well as the development of methods for integrating different data sources (e.g. in-situ, models) for a comprehensive water quality monitoring and evaluation.
• Future research may use more sophisticated methods such as machine learning and artificial neural networks instead of (linear) regression analysis.
• Adapted from World Water Quality Alliance (2021). World Water Quality Assessment:
First Global Display of a Water Quality Baseline.