MENTUM EFORMITIES IN CHIRONOMUS LARVAE

Most studies on alternations of benthic macro-in-vertebrate community structure are related to trophic (nutrient) and general pollution conditions rather than to exposure to specific persistent toxic substances. More recently, sublenthal effects in relatively tolerant-worms like Chironomid deformities in mandibles or antennae, and Oligochaete abnormalities apparently have an indicative value ot distinguish chemically polluted sediment areas. One of such approaches is available to measure morphological responses in aquatic communities to environmental perturbations including sediment contamination i.e. mentum deformity in chironmous larva.

Mentum deformity is the morphological changes in the teeth arrangement tin mouthparts of chironomid larvae due to toxic sediments. Shows the structure of normal menthm.

The family of chironomid is ubiquitous and represents the largest family of aquatic insects. These species are tolerant to the organic pollution and found in high densities in sedimentation areas where accumulation of toxic pollutants can be expected. Most contaminants in the water phase adsorb to fine organic or inorganic particles. Due to sedimentation of these particles contaminants accumulate in the sediments. Benthic chironomid from a primary link in the transmission of contaminants from sediments to the higher level of the food chain. The larval stage of chironomid are exposed to contaminant throughout the longest, most critical and metabolically active stage of their life cycle.

The study on mentum deformity of chironomus was carried out at several sites along the Yamuna River, the Agra canal, the Hindon and in some drains in the Union Territory of Delhi. The highest percentage of mentum deformities was found at downstream of Okhla Barrage (11.4%), and the lowest at downstream of Wazirabad barrage (1%) show the levels of abnormality in the mentum of chironomid at the various locations in the Yamuna.