Earthworm Diversity And Abundance In Selected Dumpsites In Ibadan, And Toxicity Of Contaminated Water On Associated Fauna

ABSTRACT

Huge quantities of wastes which are indiscriminately disposed into uncontrolled

dumpsites and flowing waters around residential areas are generated from Ibadan,

metropolis. These may adversely affect soil, surface- and ground-water qualities and

the fauna. Limited information exists on toxic effects that wastes from these nondesignated

sites have on associated fauna. Earthworms are one of the dominant fauna

in soils and are pollution bioindicators. Therefore this study was designed to

investigate physico-chemical parameters, earthworm diversity and abundance, and

acute toxicity of contaminated-water on some fauna in selected dumpsites in Ibadan.

One-hundred and twenty water samples from streams (Irefin, Gege, Gbagi, Odinjo,

and Omi-Adio) receiving domestic wastes; 60-composite soil samples each from

dumpsites (Ojokondo, Olodo, Moniya, Idi-Ope and Oremeji) and stream banks; 12-

composite soil samples from a control site at University of Ibadan (UI); 72

groundwater samples from wells around the dumpsites and UI were purposively

collected once every two months from March 2008 to February 2010. Earthworms

from top-soil were sampled using 0.25x0.25 m2 quadrat, handpicked, identified and

density determined following standard procedures. Earthworm species’ diversity and

evenness were determined using Shannon-Wiener diversity index and Shannon’s

evenness, respectively. Water samples were analysed for physico-chemical

parameters [including Dissolved-Oxygen (DO), Biochemical-Oxygen-Demand

(BOD), and Chemical-Oxygen-Demand (COD)] and soil samples including lead and

zinc using standard methods and results were compared with NESREA standards.

The 48-hour-LC50 of stream-samples were determined for Cloeon perkinsi (mayfly)

larvae (CP); while 96-hour-LC50 for Rana temporaria tadpoles, Clarias gariepinus

frys (CG1) and fingerlings (CG2) were determined using Probit method. Data were

analysed using descriptive statistics and ANOVA at p=0.05.

Three earthworm species (Eudrilus euginiae, Dichogaster modigliani and

Hyperiodrilus africanus) were identified at UI, streams and dumpsites. Highest

density of Eudrilus euginiae (30.0±13.7/m2) was recorded at UI and this was

significantly different from other sites, while lowest (6.4±2.2/m2) was recorded at

Ojokondo. Highest densities of Hyperiodrilus africanus (32.7±14.6/m2) and

Dichogaster modigliani (40.0±0.0/m2) were recorded at UI and Gbagi, respectively;

while lowest value of 4.0±0.0/m2 was recorded at Irefin and Gege. Eudrilus euginiae

UNIVERSITY OF IBADAN LIBRARY

and Dichogaster modigliani were not found at Gege and Idi-Ope, respectively, while

Hyperiodrilus africanus was not found at Odinjo, Moniya and Olodo. Earthworm

diversity (0.5) was highest in UI and lowest (0.3) at Gege. Earthworms were most

evenly distributed at Odinjo (2.4) and least at Ojokondo (0.8). The DO (mg/L) for

streams ranged from (0.4±0.4) to (2.6±0.6) and were lower than permissible limit for

aquatic life. Lead (260.6±77.7mg/kg, 269.6±46.4mg/kg) and zinc (456.9±69.9mg/kg,

1685.1±420.3mg/kg) values in Gege and Ojokondo soils, respectively were

significantly higher than NESREA limits. In all groundwater samples, BOD

(46.7±21.0mg/L) and COD (154.0±7.0mg/L) exceeded NESREA limits. The 48-hour-

LC50 of stream-water to CP (Irefin, 12.7%; Gege, 8.6%), and 96-hour-LC50 to CGI

(Gege, 0.8%; Gbagi, 2.8%) and CG2 (Gege, 3.3%; Irefin, 0.6%) indicated high

toxicity of the sites.

The low earthworm abundance, poor physico-chemical qualities and high toxicity of

the study sites revealed that the soil, streams and groundwater were polluted in

Ibadan. Consequently, there is need for adequate management and disposal of solidwastes

to prevent further environmental contamination.