Abstract:
Wetland ecosystems play a critical role in the environment. It provides global
significance environmentally, economically, and socially. Wetlands have several
important functions which include storage of carbon, storage of nutrients, retention of
sediments and pollutants. Wetlands also serve as sinks and transformators in water and
nutrient cycle. The unrestricted use of natural wetlands has posed a great concern as these
wetlands acts as sinks for point and non-point sources of pollution in surface water runoff
from municipal and agricultural sectors. These pollutants can have adverse effects on the
working of the wetland in terms of retention and removal of such pollutants. Therefore,
this study was undertaken to profile pesticide residues in Mobego-Kabianga wetland
ecosystem. In addition, the retention efficiency of pesticide residues was also
investigated. Values of physical-chemical parameters including pH, Total Dissolved
Solids (TDS), Total Suspended Solids (TSS), temperature, conductivity, dissolved
oxygen (DO) and flow rate were measured in situ at the inflows, midpoints and at
outflows to the wetland ecosystems using Lab Quest vernier caliper instrument. Water,
soil/sediments and selected plant materials samples were collected and analyzed for
residual pesticides using coupled Gas Chromatography - Mass Spectrometric/Mass
Spectrometric (GC-MS/MS) and Liquid Chromatography - Mass Spectrometric/Mass
Spectrometric (LC-MS/MS) methods. All results were recorded and analyzed for
measure of central tendencies using SAS statistical system version 9.4. From the study,
levels of physicochemical parameters ranged from 0.259-1.079 m/s (flow rate), 0.233-
10.03 mg/l (dissolved oxygen), 592-764 µs/cm (conductivity), 17-20 oC (temperature), 6-
8 (pH), 384-1646 mg/l (TDS) and 700-910 mg/l (TSS). Variation in the levels of physico chemical parameters was noted with p≤0.05. However, TSS was found to have no
significant difference with p=0.06. In analysis of residual pesticides, 24 prominent
residual pesticides were detected and quantified by GC-MS/MS and LC-MS/MS and they
include: diazinon, dimethoate, chlorpyriphos, malathion, methidathion, aldrin, BHC,
chlordane, DDT, DDD, DDE, metachlor, alachlor, dieldrin, metolachlor, aldicarb,
carbaryl, carbofuran, methiocarb, methomyl, deltamethrin, tetramethrin, pyrethrin and
cypermethrin. Their levels ranged from 0.001 to 0.861 ppb in water; 0.001 to 0.501 ppb
in sediments and 0.001 to 0.466 ppb in plant materials. The calculated retention
efficiency was 85 %. However, cypermethrin and dieldrin recorded negative retention
efficiency. Significant variation was observed in levels of physicochemical parameters,
residual pesticides and retention efficiencies of the wetland ecosystem. It is
recommended that a study be carried out to develop environmentally friendly molecules
which can be used for pest control and management practices with an aim of protecting
wetland ecosystems from effects of chemical pesticides and hence improve retention
efficiencies of natural tropical wetland ecosystems.
