1.1 General Introduction
A pollutant is any substance in the environment, which causes objectionable effects, impairing the welfare of the environment, reducing the quality of life and may eventually cause death. Such a substance has to be present in the environment beyond a set or tolerance limit, which could be either a desirable or acceptable limit. Environment is defined as the totality of circumstances surrounding an organism or group of organisms especially, the combination of external physical conditions that affect and influence the growth, development and survival of organisms (FarlexIncorporated, 2005). It consists of the flora, fauna and the abiotic components, and includes the aquatic, terrestrial and atmospheric habitats. The environment is considered in terms of the most tangible aspects like air, water and food, and the less tangible, though no less important, the communities we live in.
Comprising over 70% of the Earth‟s surface, water is undoubtedly the most precious natural resource that exists on our planet (Terry, 1996). Population growth, urbanization and industrialization have led to rapid degradation of the environment and publichealth due to improper sewage disposal, especially in developing countries. Conventional solutions are inappropriateand expensive because the infrastructures and skilled labour are lacking.
The development of the intensive agriculture in Nigeria between 1960 and
1990 totally neglected the aspect connected with the negative impact of the
chemical compounds toxic on the air, water and soil. As one of the consequences
of heavy metal pollution in soil, water and air, plants are contaminated by
heavy metals. Contamination of the aquatic environment by the heavy metals
has become a serious concern in the developing world(Chandra et al., 1997). Heavy metals unlike organic pollutants are the persistent in nature, therefore, tends to accumulate in the different components of the environment (Chandra et al., 1997). Sources of metals in the environment are widespread and data on typical concentrations in the various media and environmental settings exits worldwide (Mwamburi, 2015).These metals are released from a variety of sources such as mining, urban sewage, smelters, tanneries, textile industry and chemical industry.
Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans, aquifers and groundwater). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds. Aquatic environments are increasingly affected by human activity because of urban, industrial, mineraland agricultural waste. The use of the ocean as a dumpingground for wastes could lead to high levels of pollution in the aquatic environment (Bramha et al.,2014; Bodin et al., 2013). Water pollution affects plants and organisms living in these bodies of water. In almost all cases, the effect is damaging not only to individual species and populations, but also to the natural biological communities.
Water pollution is a major global problem which requires ongoing evaluation and revision of water resource policy at all levels (international down to individual aquifers as well). It has been suggested that it is the leading worldwide cause of deaths and diseases and that it accounts for the deaths of more than 14,000 people daily(Pink, 2006; West, 2006).
The specific contaminants leading to pollution in water include a wide spectrum of chemicals and pathogens. While many of the chemicals and substances that are regulated may be naturally occurring (calcium, sodium, iron, manganese, etc.) the concentration is often the key in determining what is a natural component of water, and what is a contaminant. High xxiv
concentrations of naturally occurring substances can have negative impacts on aquatic flora and fauna. Oxygen-depleting substances may be natural materials, such as plant matter (e.g. leaves and grass) as well as man-made chemicals. Other natural and anthropogenic substances such as may cause turbidity (cloudiness) which blocks light and disrupts plant growth, and clogs the gills of some fish species (EPA, 2005).
EFFECTS OF COPPER AND LEAD ON THE PHYSIOLOGY OF SALVINIA MOLESTA, PISTIA STRATIOTES AND LEMNA TRISULCA AND THEIR PHYTOREMEDIATION POTENTIALS