Abstract
The purpose of this research was to monitor the distribution of Cd, Cr, Cu, Ni, Pb and Zn in plants of Lagos lagoon wetlands in Nigeria. Water, soil and dominant plants were collected from 46 sampling points for a period of 1 year and analysed using ICP-AES. The order of heavy metals presence in soil samples was as follow: Zn>Cr>Cu>Pb>Cd>Ni. The Zn concentration was the highest whereas the lowest concentration was Ni. All water samples showed varying degrees of contamination across all the sampling points in these wetlands. A greater percentage of all metals concentration for Pb, Cd, Cr and Ni were higher than the permissible limit set by World Health Organisation. Pb ranged from 0.01±0.00 to 0.91±0.04 mg/L, Cd from 0.01±0.00 to 0.31±0.02 mg/L, Cr from 0.05±0.00 to 1.15±0.01 mg/L, Ni from 0.01±0.00 to 0.52±0.03, Cu from 0.21±0.01 to 1.11±0.01 mg/L and Zn ranged from 0.15±0.00 to 10.28±0.02 mg/L. The median values of each metal that the shoots and roots of individual plants accumulated metals in the order: Zn>Cu>Pb>Cr>Ni>Cd. Ipomea aquatica had the highest concentration of Pb in its shoot (1.12 mg/kg) while Ludwigia adscendens had the least (1.12 mg/kg) in its shoot. Pb level in the roots was highest in Eichonia crassipe s (5.69 mg/kg). The highest level of Cr in shoot (2.23 mg/kg) and root (5.41 mg/kg) was observed in Commelina benghalensis while Cr concentration is lowest in the shoot (0.04 mg/kg) and root (0.18 mg/kg) of Althernathera philoxerrides. Ludwigia adscendens had the lowest concentration of Ni in its root (0.01 mg/kg). The highest shoot concentration of Cu (4.21 mg/kg) was observed in Eichonia crassipes while Ipomea aquatica had the lowest concentration in its shoot (0.23 mg/kg). Paspalum vaginatum ’s root had the highest Cu concentration (12.32 mg/kg) while lowest concentration of Cu was observed in the root of Sagittaria sagittifolia (0.69 mg/kg). Transfer factors for most of the plants species were less than 1, indicating that metals accumulated by these plants were largely retained in the roots. A. philoxerrides had translocation factor greater than one for Ni (10.30), while for Cr was 1.25 and 1.40. This present findings indicate that, despite ecological similarities, the different plant species tend to respond differently to exposure to heavy metals and also in their ability to accumulate the various metals. Thus, heavy metals sequestration from the soil to these plants characterized them as metals pollution indicators. Keywords : wetland plants, heavy metals, biomonitoring, bioaccumulation capacity, translocation factor
Highlights
Nigeria is richly endowed with large numbers of wetlands ecosystem, and the Lagos lagoon has been identified as one of the fourteen major wetland belts in the country (Oyebande, et al, 2003; Asibor, 2009)
A study by Ghavzan et al, (2006) demonstrated that Pistia stratiotes was associated with high pollution rates in water bodies, while Niaz and Rasul (1998) showed that Pistia stratiotes and Eichhornia crassipes could be used as biological indicators in wetland habitats
The aims of this paper are to investigate the amount of heavy metals in dominant plants species collected from Lagos lagoon wetlands; and to assess the opportunity of using these aforementioned plant species as indicators of the aquatic ecosystems pollution level with heavy metals and their feasibility for phytoremediation
Summary
Nigeria is richly endowed with large numbers of wetlands ecosystem, and the Lagos lagoon has been identified as one of the fourteen major wetland belts in the country (Oyebande, et al, 2003; Asibor, 2009). Among the worst environmental contaminants are the heavy metals (Njoku et al, 2013) They are serious pollutants due to their toxicity, persistence in natural conditions and ability to be incorporated into food chains (Akinola et al, 2008; Adesuyi et al, 2015b). Wetlands as an ecosystem is characterized by the presence of plants that are adapted to life in the soil formed under saturated conditions (Mitsch and Gosselink, 1993). Some of these plants include Alternanthera philoxeroides, Commelina benghalensis, Eichhornia crassipes, Enhydra. Fluctuans, Ipomoea aquatica, Ludwigia adscendens, Sagittaria sagittifolia Pistia stratiotes and the sedges These plants enable the direct assessment of the response of wetland vegetation to changes in aquatic discharge. The aims of this paper are to investigate the amount of heavy metals in dominant plants species collected from Lagos lagoon wetlands; and to assess the opportunity of using these aforementioned plant species as indicators of the aquatic ecosystems pollution level with heavy metals and their feasibility for phytoremediation
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