INSECTS that were introduced tostem the spread of water hyacinth arebeginning to avoid feeding on theweed because they are polluted bytoxic metals. However, the insectsseem to be developing resistance tothe toxicity by producing new cellular proteins and synthesizing newones.
In experiments conducted by scientists -at the.Indian Institute ofC210mical Technology in Hyderabad,water hyacinth (Eichhorniacrassipes) plants were kept for aweek in solutions containing variousamounts of cadmium, zinc, mercurysad manganese. The maximumabsorption of metals by the plantsa=arred in the first 24 hours, aftervMch the uptake was gradual.The accumulation of metals wasHeight in the roots, compared toOther parts.
The plants absorbed metals withNo apparent deleterious effects.However, when very high concentration of metals were absorbed, theLeaves turned pale and plant growth was restricted.
When water hyacinth weevils(Neochetina eichhornae) fed on theplants they absorbed high quantitiesof cadmium and zinc but lowamounts of mercury and manganese.Adult weevils that fed on contaminated plants did noi show any toxicsymptoms - even when contamina-tion was high - suggesting they wereable to develop mechanisms to resistmetal contamination. The insectsmay have survived the toxicity byphysiological avoidance, but prolonged exposure to the metals couldresult in genetic changes.
Studies showed the accumulationof metals in insects led to the disappearance of some normal proteinsand the emergence of new ones.Scientists are unsure of the changesthe new proteins,could cause butthey may be responsibIq for metaldetoxification by binding metal ionsand rendering them less.harmful.
The scientists found high accumulation of chromium - found inplenty in wastes from dyeing, tanning, explosives, ceramics, textile,paint and paper industries - in thewater hyacinth and the water lettuce.This led to increased respiration,yellowing of leaves and the inhibition of chlorophyll synthesis,affecting the process of photosynthesis.