Distribution of organochlorine pesticides in macroinvertebrate functional feeding guild (FFG) of predators, Rhagovelia spp. in a tropical estuarine ecosystem

Abstract

The current world population stands at approximately 8.5 billion people and this number is likely to shoot up in the coming decades. This increased trend in world population demands for sufficient food,

which calls for, improved agricultural production systems. In order to achieve this, a tremendous in- crease in pesticide application of about 30-40% has been documented and this trend is predicted to

increase in the coming years. Due to their negative impacts to the environment, some pesticides main- ly those of organochlorines (OCPs) have since been banned, but their residues can still be detected in

different media causing deleterious effects on organisms. The aim of this study, therefore, was to assess the distribution of organochlorine pesticides (OCPs) by aquatic macroinvertebrates FFG of Rhagovelia

spp. in the tropical estuarine ecosystems of South Coast, Kenya. Twelve sampling stations were purpo- sively identified taking into considerations different hydrological and ecological factors. Rhagovelia spp.

were sampled using established methods and analysis for OCPs detection were performed using a TSQ

Vantage Triple-Stage Quadrupole Mass Spectrophotometer (Thermo Electron) equipped with a heat- ed electrospray ionization probe (HESI-II). Separation, detection, identification and quantification of tar- get analyses followed the same established methods. Sixteen OCPs were recorded in Rhagovelia spp.

samples collected from all the 12 sampling stations. γ-HCH was the lowest (2.74 0.18 ng g-1 dw) recorded concentration value for OCPs from Rhagovelia species samples whereas OCPs Cis_chlordan, mirex, p,p’_DDT, p,p’_DDE, o,p’_DDE and HCH recorded 10.09 0.35 ng g-1 dw, being the highest registered value. Analysis of variance (ANOVA) on the mean concentration residues of OCPs in Rhagovelia spp. samples yielded a significant variation among the sampled stations (F = 77.79, df = 11, p < 2.2e-16). The statistical

analysis revealed that each station played a crucial role in determining the levels of OCPs in Rhagove- lia spp. due to environmental factors, early life history strategies of the tested bioassay organism, and

different sources of OCPs as influenced by anthropogenic activities. The study recommends for

the application of macroinvertebrate FFG of Rhagovelia spp. in biomonitoring of estuarian eco- systems. The study also recommends the use of different FFGs of macroinvertebrates such as

grazers, collector-gatherers, filterers and shredders in order to bring out the general behavior of these pesticides along the food web.