Comparative Evaluation of Domestic Sewage and Well Water Irrigation on the Mineral Profile, Nutritional, and Nutraceutical Attributes of Cajanus cajan (L.) Millsp.
Abstract
Water scarcity has severely impacted the global economy, livelihoods, and environmental quality, driving the use of municipal and industrial wastewater as an alternative irrigation source in urban and peri-urban agriculture. This practice addresses water deficits but raises concerns about risks to human and environmental health from contaminants. This study evaluated the effect of diluted domestic sewage wastewater (used in semi-urban Palakkad) versus well water (used in rural areas) on pigeon pea (Cajanus cajan). We conducted a comprehensive analysis of irrigation water, soil, and various plant parts (seeds, leaves, stems, pods) for physicochemical parameters, proximate composition, full mineral profile, heavy metals, and in vitro antioxidant activity. Results indicated that most physicochemical parameters of the irrigation water were within FAO permissible limits, though the semi-urban source showed elevated iron, phosphate, and alkalinity. Critically, concentrations of toxic heavy metals (Ni, Cr, Cd, Pb, Cu) in soils and, most importantly, in the edible seeds remained well below WHO/FAO safety thresholds. Proximate analysis confirmed good nutritional quality in seeds from both sources (e.g., protein: 15.5-17.6 g/100g). Plants irrigated with both water types exhibited significant in vitro antioxidant activity across five complementary assays (FRAP, DPPH, ABTS, Metal Chelating, NO Scavenging), which was strongly correlated with phenolic content. A notable finding was the elevated iron content in seeds, suggesting a natural bioaccumulation propensity in C. cajan. The study concludes that, under the observed conditions, the use of diluted domestic sewage wastewater did not induce harmful heavy metal accumulation in C. cajan, maintained its nutritional value, and preserved its bioactive potential. This supports its role as a viable and sustainable irrigation alternative, contributing to water security and nutrient recycling. Non-seed tissues (leaves, pods) showed high phenolic content, indicating value for nutraceutical use or animal feed.
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Introduction
The global population is expected to exceed nine billion people by 2050. Population increases are expected to further increase water usage and wastewater production. The world is facing a water quality crisis resulting from continuous population growth, urbanization, land use change, industrialization, food production practices, increased living standards, unsustainable water use practices and wastewater management strategies. Freshwater resources are continuously depleting overtime due to a combination of climatic, political, and anthropogenic factors. This growing scarcity has compelled many farmers to use sewage water as an alternative irrigation source for cultivation. Wastewater has a direct impact on the biological diversity of aquatic ecosystems and its inappropriate management is capable of disrupting the fundamental integrity of life support systems, on which a wide range of sectors, from urban development to food production and industry (Buonocorea et al., 2016; Khan et al., 2025). Website: www.ijoear.com Journal DOI: 10.25125/agriculture-journal Use of domestic and industrial wastewater in agriculture for irrigating crops appears to be a lucrative option. Besides being a source of irrigation water, these waste waters contain appreciable amounts of plant nutrients. In India, total wastewater generated per annum from 200 cities is about 2600 Mm3 and also the use of sewage effluents for irrigating agricultural lands is on the rise, especially in the peri-urban area. The increasing demand for freshwater, driven by rapid urbanization and residential development, has intensified pressure on existing water resources. Consequently, the use of sewage water for irrigation in agricultural practices has become increasingly common. This trend substantially alters the physicochemical characteristics of natural water bodies, generates significant economic activity, and supports numerous livelihoods, particularly among socioeconomically disadvantaged farming communities. However, the reuse of wastewater in agriculture presents several environmental and health-related risks. Some impacts are short-term, such as contamination by microbial pathogens, while others are long-term, including the gradual accumulation of salts and heavy metals in the soil, which can adversely affect soil fertility and crop productivity. The controlled reuse of treated wastewater offers a potential strategy to mitigate pressure on conventional freshwater resources by redirecting part of this water for agricultural and industrial applications. The nutrient content present in treated wastewater can enhance plant growth, thereby transforming potential pollutants into valuable resources. Given that the agricultural sector accounts for approximately 92% of global freshwater consumption, wastewater reuse represents a pragmatic approach toward sustainable water management. Nonetheless, in many regions, untreated sewage and industrial effluents are directly discharged onto agricultural lands and used for cultivating crops, including vegetables, posing considerable ecological and public health concerns (FAO, 2010; Liu et al., 2015; Balkhair and Ashraf, 2016; Shakir et al., 2017).
The utilization of wastewater treatment plant effluents for irrigation in agricultural and green areas offers several significant advantages, including cost-effectiveness, year-round availability, and reduced treatment and disposal expenses (Ganji et al., 2024). These effluents are often rich sources of organic matter and essential plant nutrients, which can enhance soil fertility and crop productivity. However, their continuous application can also lead to the accumulation of heavy metals such as Fe, Mn, Cu, Zn, Pb, Cr, Ni, Cd, and Co in the receiving soils. The elevated concentrations of these metals pose serious environmental and health concerns, as they may enter the food chain through the cultivation of edible crops. Consequently, the consumption of food grown using sewage wastewater irrigation increases the potential risk of heavy metal exposure to the general population. (Surdyk et al., 2025; Siddhuraju et al., 2025)
Pigeon pea (Cajanus cajan) is an important grain legume cultivated and consumed extensively across tropical and semi-arid regions of the world, including Asia, Africa, Latin America, and the Caribbean (Fatokimi andTanimonure, 2021). The crop exhibits strong adaptability to rain-fed conditions owing to its deep root system, heat tolerance, and rapid growth rate, which make it particularly suitable for cultivation in semi-arid environments. Globally, pigeon pea ranks as the sixth most important legume, occupying approximately 5.4 million hectares, with an estimated annual production of 4.49 million tons. It is commonly fried with spices, consumed as germinated seeds either raw or cooked, or combined with cereals to enhance nutritional value. Pigeon pea offers multiple agronomic and nutritional benefits, serving as botha valuable source of human food and animal feed while also contributing to soil fertility enhancement through nitrogen fixation. Nutritionally, pigeon pea seeds are rich in protein (20–22%), fat (1–2%), carbohydrates (approximately 65%), and ash (6.8%), and they provide considerable amounts of dietary fiber and essential minerals. Moreover, pigeon pea is recognized for its high content of bioactive phenolic compounds, including total phenolics, total flavonoids, and strong antioxidant activity. The seed protein of pigeon pea exhibits favorable functional properties such as solubility, water-and oil-absorption capacity, emulsification, and foaming, which enhance its potential for use in various food formulations. (Anjulo et al., 2020; Haji et al., 2024). C. cajan is widely distributed throughout the tropics as a pulse crop, mainly for grain and also as a cover crop or green manure crop. It is drought-tolerant and has better adaptation to poor soil condition than most tropical legumes. The foliage contains crude protein and fat contents of 20.2% and 1.7%, respectively. These legumes are classified as minor grain legumes because they are underutilized as human food in Nigeria due to the long hours of cooking them before consumption. However, utilization could be expanded because they are sources of dietary protein. They are indigenous and usually cultivated in association with arable crops like yam and cassava. Large biomass of these legume foliage is produced annually (Ajayi, 2011). C. cajan, among legumes, has an important place in the diet of many people in the world. It is one of the oldest food crops. India alone contributes over 90% of the world'spigeon pea production. It is also a food crop in many other tropical countries and is commercially important in East Africa, the Caribbean, and Latin America. Different parts of this plant are used in traditional medicine in China and Brazil. The antioxidant, antidiabetic, antimicrobial, DNA damage protective and xanthine oxidase inhibitory properties of this plant are generally established. Extracts from this crop are reported to be effective for the Website: www.ijoear.com Journal DOI: 10.25125/agriculture-journal treatment of diabetes, dysentery and hepatitis. Leaves have been useful for the treatment of wounds, bedsores, malaria and diet induced hypercholesterolemia, whereas the seeds are sedative and used to treat cough, hepatitis, plasmodial diseases and diabetes. Inmost of these cases, the effector molecules need to be identified and characterized. Chemical investigations have been successful in bringing out the major molecules from each part of the plants, especially the leaves and seeds. Leaves are rich in polyphenolic com-pounds such as luteolin and apigenin, flavonoids such as genistein and genistin, anticancerous antiflavone cajanol, stilbenes such as cajaninstilbene acid (CSA) and pinostrobin, antibacterial coumarin cajanuslactone and cajaminose, phenylalanine, and hydroxybenzoic acid with anti-sickle cell disease effects (Mathew et al., 2017). Considering the escalating global reliance on wastewater irrigation as an alternative water resource, it is imperative to evaluate its implications for soil and water quality, as well as for the safety of crops cultivated under such conditions. Domestic wastewater, derived mainly from household activities, generally contains lower industrial contaminants and provides a richer balance of essential nutrients and organic matter than mixed sewage wastewater, while offering greater soil fertility benefits than treated sewage effluents, which often lose nutrient content during treatment. These characteristics make domestic wastewater a potentially valuable resource for enhancing soil nutrient status, improving microbial activity, and supporting better crop growth and yield with reduced dependence on chemical fertilizers. Accordingly, the present study was undertaken to investigate the environmental and food safety aspects associated with pigeon pea cultivation using domestic sewage wastewater. This research aims to provide scientific insights into the sustainability of wastewater reuse, recycling, and recharge from domestic sewage systems for agricultural purposes, while also elucidating the broader implications for soil health, crop productivity, and public health. The study was conducted in selected urban agricultural fields of Palakkad, Kerala, with a comparative assessment of pigeon pea cultivated under well-water irrigation within the same agroecological zone. While previous research has often focused on the impact of industrial or mixed wastewater, there is a distinct lack of comprehensive studies assessing the effects of domestic sewage wastewater—which has a different nutrient and contaminant profile—on the safety and quality of a multipurpose crop like C. cajan. This study aims to fill this knowledge gap by conducting a comparative evaluation of C. cajan cultivated using diluted domestic sewage wastewater (semi-urban site) and conventional well water (rural site). We comprehensively assess: (1) water and soil quality parameters, (2) the translocation of essential minerals and heavy metals into various plant tissues, (3) proximate nutritional composition, and (4) the profile of bioactive compounds and associated in vitro antioxidant activities. The findings will provide a scientific basis for the safe reuse of domestic wastewater in sustainable legume cultivation, with implications for food security and resource management.
Conclusion
This comprehensive study provides robust evidence that the use of diluted domestic sewage wastewater for irrigating C. cajan, under the specific conditions of this preliminary field assessment, did not result in the dangerous accumulation of toxic heavy metals (Cd, Pb, Cr, Ni, Cu) in the edible seeds. All measured values remained well within international food safety standards. Website: www.ijoear.com Journal DOI: 10.25125/agriculture-journal The irrigation water, while nutrient-rich and high in iron, was not contaminated with problematic levels of industrial pollutants. The proximate nutritional quality of the seeds—their protein, carbohydrate, and energy content—was maintained and was comparable to seeds grown with well water.
Furthermore, the plants retained significant levels of bioactive phenolic compounds and associated high in vitro antioxidant activity, which was strongly correlated. The elevated iron content in seeds warrants further study but appears to be a varietal or physiological trait rather thana contamination issue. The non-seed biomass (leaves, pods) showed particularly high phenolic content, indicating valuable by-products.
Therefore, with necessary precautions—primarily the ongoing monitoring of water quality (particularly for salts and Fe) and soil health—the controlled use of diluted domestic sewage wastewater can be considered a viable and sustainable irrigation alternative for pigeon pea cultivation. This practice supports critical goals of water conservation, nutrient recycling, and urban food security without compromising the safety or nutraceutical value of this important legume crop. Further long-term studies under varied field conditions are recommended to validate these promising findings.
AUTHOR CONTRIBUTIONS Dhanya Viswanathan: methodology, investigation, data curation, formal analysis, writing–original draft. Velukutty Amrutha: investigation, data curation, conceptualization, writing – review and editing. Perumal Siddhuraju: methodology, conceptualization, data curation, supervision, project administration, writing – review and editing.