The effects of different detergent concentrations on seed germination and plant growth of Amaranthus hybridus L., Solanum lycopersicon L. and Abelmoschus esculentus L. were investigated. Three brands of commercial laundry detergents were used to prepare the irrigation solutions. For each detergent brand, three different detergent concentrations were prepared: 1.0g/l, 2.5g/l and 5.0g/l. Water without detergent served as the control. The germination study was carried out in Petri dishes while plant growth studies were done using polyethylene bags filled with 6kg of soil. The results from the studies showed that the presence of detergents in the watering solutions significantly reduced seed germination in the three plants. The inhibition of germination was found to increase as detergent concentration increased. Among the three test plants, A. hybridus seeds showed the highest sensitivity to the detergent solutions, as their germination (%) was 0% at detergent concentrations of 2.5g/l and 5.0g/l. Plant growth studies also revealed that at low detergent concentrations (1.0g/l), plant growth was stimulated but as detergent concentrations increased, there was reduction in plant growth. 5g/l of the different detergents inhibited growth of the test plants. A. hybridus plants irrigated with 5g/l of the detergent solutions did not survive beyond 6 weeks after planting (WAP) while though S. lycopersicon and A. esculentus treated with 5.0g/l of the detergent solutions survived, there were significant reductions in their shoot height, leaf area, number of leaves per plant, chlorophyll content of leaves and fresh and dry biomass when compared with the control. A. hybridus was less tolerant to the stress brought about by the different detergent concentrations. Also, it was observed that the detergent treatments led to increase in soil pH, electrical conductivity and salinity which constituted sources of stress to the plants. The present study has shown that high detergent concentrations inhibit seed germination and plant growth in the plants studied.

Human activities are always accompanied with products which pollute the environment to varying extents.  Only very few of these products are not pollutants. This is the reason why environmental study is becoming increasingly necessary for the survival of plant and animal life, and ultimately humankind itself (Yahaya et al., 2011). A culprit for environmental pollution should not be sought only in outdated or new technologies (Branislav et al., 2010). Sources of pollution can be, which is so often ignored, some domestic processes in the environment such as hygiene. The subject of this study is pollution resulting from everyday hygienic procedures, specifically the use of detergents to wash household items.

1.1       What are Detergents?
            Detergents are materials which aid in the removal of dirt or other foreign matters from contaminated surfaces (Yahaya et al., 2011). They have the ability to remove dirt from porous surfaces (such as fabrics and clothes) and non porous surfaces (such as metals and plastics). Because of this, detergents are widely used in both industrial and domestic premises. They are used to wash clothes, vehicles, equipment, installations and heavy duty machines. They are also used in dispersing oil spills at sea and in pesticide formulations for agricultural purposes (Lightowlers, 2009).
Until the 1940’s, soap was the only important cleaning agent in the market but today soap is but one of the numerous cleaning products. Detergents differ from soaps in that they do not form a scum with the salts in hard water (Khurana, 2002).
According to an ancient legend, soap derives its name from Mount ‘Sapo’ in Italy where animals were sacrificed to appease the gods. The mixture of the melted animal fats and wood ashes that ran down to the clay soil near Tiber River at Mount ‘Sapo’ was found to make washing easier than ordinary water for women inhabiting the area. Another report stated that soap-making dates back to about 1500BC when a combination of animal vegetable oils and alkaline salt was used to form a soap-like material (Yahaya et al., 2011). However, modern technology has led to the creation of soapless/synthetic detergents that have gradually replaced soap in the laundry.
            During the World War II, the shortage of fats from which soap is made spurred the development of synthetic detergent. After the war, the need for new types of detergents for automatic washing machines accelerated the trend. The first detergent was used chiefly for hand-dish washing and fine fabric laundering. This was followed by the development of multipurpose laundering detergent introduced in the USA in 1946. Today, the detergent market is now highly competitive where different brands compete with one another to get customers (Khurana, 2002).
Earlier, detergents were made by treating an aromatic or benzene type compound with sulphuric acid followed by neutralization with alkali to convert the product to its sodium salt. These detergents however became a public nuisance because unlike soaps, they were neither soluble nor biodegradable; that is once put into water they tended to remain there, resisting conversion into less complex and more soluble substances. The aromatic compound was later replaced with a so called linear alkyl type compound in the process described above and the detergent produced was as effective as the former kind in its detergent action and was more biodegradable.

1.2       Detergent Composition
            Detergents compose of surfactants, builders, alkalis, enzymes, anti-redeposition agents, active oxygen bleaches, anti microbial agents, fabric softeners, fragrances, optical brighteners, preservatives, foam regulators, hydrotropes and processing aids (Smulders, 2002).

1.2.1    Surfactants
            Surfactants are the active cleaning agents in the detergents. Surfactants are also known as surface active agents because they act upon a surface. They perform three major roles:
i)                    Penetrating and wetting fabric
ii)                  Loosening soils/dirt (assisted by the mechanical action of the hand or washing machines)
iii)                Emulsifying soils and keeping them suspended in the wash solution.
Surfactants have two domains within one molecule, a polar hydrophilic (‘water loving’) head group and a non polar hydrophobic (‘water hating’) tail. Their polar group forms hydrogen bond with water molecules, while the hydrophobic tail aggregates due to hydrophobic interactions. Because of the nature of surfactants they are able to dissolve in water and at the same time to solubilize hydrophobic compounds in water (Sharma, 2009). Surfactants are either derived from petrochemicals or vegetable oils or combination of these sources. Surfactants used in detergents are of three main types: anionic, non-ionic and cationic. Anionic surfactants are the most common surfactants in laundry detergents. They are highly effective in emulsifying oil and clay soils. Some examples are linear alkyl sulphonates (LAS), alkyl aryl sulphonates such as dodecylbenzene sulphonate (DDBS) and alcohol ether sulphates such as sodium lauryl ether sulphate (SLES). Surfactants in detergents are toxic to aquatic life; persist in the environment and breakdown into additional toxic byproducts (Tomislav and Jasna, 2010).
1.2.2    Builders
            Builders are key detergent components which remove the calcium and magnesium ions present in hard water, thus lowering the concentration of surfactants necessary to perform the detersive action.
            Sodium tripolyphosphate(STPP) is the most widely used builder in detergents. Other builders used include sodium carbonate, Zeolites and sodium disilicates. STPP and other forms of phosphate builders could lead to algae blooms when released into water body and consequently leading to deoxygenation of the water body (Morse et al., 1994).
1.2.3    Alkalis
            They raise the pH of the laundry wash water, which assists in breaking up oily and acidic soil components. Common alkalis used in laundry detergents include sodium carbonate, sodium bicarbonate, sodium silicate, sodium citrate and ammonium hydroxide.
1.2.4    Enzymes
            They aid in effective stain removal and also provide colour and fabric care. The most commonly used enzymes are proteases (which break down proteins), amylases (which break down starch) and lipases (which break down fats) (Smulders, 2002).
Other constituents of detergents include anti-redeposition agents, active oxygen bleaches, anti microbial agents, fabric softeners, fragrances, optical brighteners, preservatives, foam regulators, hydrotropes and processing aids (Smulders, 2002).

1.3       Justification for the Study
            The increasing environmental pollution arising from detergent use is becoming a growing concern. Lack of information on the effects of detergent on living organisms makes people to handle or dispose detergents carelessly. Therefore, a thorough investigation on the ecological disorder that may arise from improper handling or disposal of detergents needs to be done. This is necessary because there is no alternative to detergent for now.
            Worldwide, governments are making concerted efforts to keep environments free of pollutants through policies, environmental conferences and conventions. In Nigeria, the Federal Government is emphasizing the need for adequate environmental protection in any technological and socioeconomic development by strictly asking industrial operators to control the effects of their wastes (DPR, 1991). But in Nigeria and other countries, only few chemicals have been ecologically tested for safety despite their alleged environmental and ecological impacts (Ogundiran et al., 2010).
            Also, grey water reuse in agriculture seems to be the most explored strategy in most water management programmes (Jury and Vaux, 2007). Grey water includes all washing domestic water produced with the exception of the toilet water. Despite its apparent clarity, these waters should not be used directly on crops without sufficient treatment as it is often the case (Gross et al., 2007).Generally grey water is the result of the using of detergents, vegetable oils, soaps, water and other kitchen and washing residues (Sawadogo et al., 2014). Indeed, grey water is often a source of elevated levels of compounds such as surfactants, oils, boron and salt which can alter soil properties, damage plants and contaminate groundwater (Travis et al., 2008; Wiel-Shafran et al., 2006). Surfactants in prepared irrigation solutions with detergent water have been recognized as a major contributor to the reduction of hydraulic conductivity of soils and as components that can lead to water repellent soils with adverse impacts on agricultural productivity and environmental sustainability (Lado and Ben-Hur, 2009; Shafran et al., 2005). When untreated grey water is used to irrigate plants growing in soil, the fate of surfactants in grey water irrigated soil-plant systems is not well known (Misra et al., 2012).
            These days, it is common practice for people to grow vegetables near their houses so that they can have a ready supply of fresh vegetables. It has also been observed that detergents from laundry water are often released to meet the needs of these plants and yet there is insufficient knowledge on what effects these detergents could have on these crop plants.
            Also there are numerous examples of polluted rivers and lake with industrial detergents. For example, the Asa River in Ilorin, Kwara State, Nigeria was reported to be polluted with industrial detergents (Adekola and Eletta, 2007). Also, it was found out that the Capsian Sea water and Volga Terek and Sulak rivers were extremely polluted with a high detergent concentration (Korshenko and Gul, 2005). Likewise the coastal zone of the sea of Okhotsk and Avacha Bay in Russia were reported to be polluted with detergent water in the North-West Coast (Zhuravel et al., 2004). And in most cases water from these sources are used in gardening for watering vegetables for human consumption. Only little is known on the effects the detergents present in these irrigation solutions would have on the plants.

1.4       Objectives of the Study
            The overall aim of the study is to determine the effects of different detergent concentrations on the germination and growth of three common tropical vegetables namely African Spinach (Amaranthus hybridus L.), Tomato (Solanum lycopersicon L.) and Okra (Abelmoschus esculentus L.). The specific objectives of the study are to:
i.        evaluate the effects of varying detergent concentrations on the germination of African Spinach (Amaranthus hybridus L.), Tomato (Solanum lycopersicon L.) and Okra (Abelmoschus esculentus L.) seeds.
ii.      evaluate the effects of different detergent concentrations on growth parameters such as plant height, leaf area, number of leaves per plant, chlorophyll content, time of flowering, weight of fruit / stem and root of the selected plants (Spinach, Tomato and Okra).

iii.    determine the changes caused by detergent pollution on the physical and chemical properties of soil, such as electrical conductivity (EC), pH, cation exchange capacity (CEC), carbon, nitrogen, phosphorus, magnesium, sodium and potassium.

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