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 crassipes
(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.
