Impact of Pesticides on Invertebrates in Aquatic Ecosystem

Introduction

The main routes through which the pesticides are transported to water bodies include surface runoff, tile drains, groundwater and leakage from point sources (Schulz, 2004). The transport pathways are strongly governed by climatic and geological conditions of the area and also by the physicochemical properties of the pesticide compound (Figure 1).

Figure 1.

Major transport routes into receiving streams for pesticides that are applied to agricultural fields

Consequently, peak pesticide concentration lasts for short period and occurs during heavy precipitation. The maximum exposure concentration is important for estimating ecological effects (Schulz & Liess, 2000). The combination of extensive agricultural activities and the close connectivity between land and stream makes them more vulnerable to pesticides. Overall, many environmental factors that act on stream ecosystems are directly or indirectly correlated. Pollutants like pesticides have potential impact on agricultural streams and are effected by other local stressors like channelisation and dredging (MacArthur & Wilson, 1967). The stream ecosystem is also influenced by the local factors which are believed to be more important for aquatic biodiversity (Pedersen & Friberg, 2009). The aquatic biodiversity is very sensitive to different xenobiotic substances like pesticides. Pesticides are believed to have more impact on invertebrates as compared to other pollutants (Beketov & Liess, 2012).

Some pesticides have severe impact on organisms even at low concentration while some are less toxic even at high concentration although it depends on the chemistry and properties of the pesticide. Synergetic effects are generally shown by different compounds with similar mode of action, and mostly trigger the effect on the exposed organism (Belden & Lydy, 2000). Few studies have shown that pesticides possess joint toxicity on aquatic invertebrates (Belden & Lydy, 2000). Bailey and coworkers (1997) showed that two organophosphorus insecticides, diazinon and chlorpyriphos, exhibit additive toxicity to Ceriodaphniadubia. Additivity between diazinon and chlorpyriphos is reasonable given that both are metabolically activated organophosphorus insecticides and act similarly with respect to binding with acetylcholine acetrase (AChE) (Ecobichon, 1991).

Indiscriminate use of pesticide spraying may cause ecological disturbance in natural aquatic environments. Lack of information about pesticide is the serious concern for ecosystems. Although mode of action of several pesticides is known (Ecobichon, 1991), however very little is known about their toxicity. Liess & Schulz (1999) and Schulz & Liess (1995) observed runoff-related insecticide input on stream invertebrate dynamics. It is confirmed from different studies that different species disappeared in macroinvertibrate community due to toxicity of pesticides (Liess & Schulz, 1999; Schulz & Liess, 1999). Hydraulic stress during runoff events was reduced in microcosms operated in the bypass to the stream (Liess & Schulz, 1999). Moreover, hydraulic stress plays synergetic role in population reduction, especially whereas the agricultural insecticide input change the dynamics of the total macroinvertebrate community and cause a serious threat to the stream ecosystem.