Aquatic weeds and their utilization 375constructed wetlands located in the tropics. The plant productivity was
accordingly high and beneficial for reuses.
7.8 Health hazards relating to aquatic weeds
The cultivation of aquatic weeds may cause health problems by:
- Contamination of the people who work in the aquatic pond
operation with pathogens in the water, - Contamination of the plants with pathogens and toxic materials such
as heavy metals and pesticides, and - Providing habitats (pond & plants) for various vectors.
Concerning the first and second health problems, the risk of contacting
pathogens by workers and contamination of plants with pathogens can be
minimized if the waste is adequately treated to eliminate pathogens before
applying to aquatic plants. This step is necessary as pathogen removal in an
aquatic system is not very effective. Direct fertilization of aquatic weed ponds
with nightsoil should be avoided as the risk is high and it reduces the
acceptability of the product.
The third health problem involves the possibility of disease transmission
through infection by metacercariae, (infective stage) which has its intermediate host
in the pond, such as snails (in case of Schistosomiasis) or attached to the plant
leaves and stems. According to Feachem et al. (1983), the parasitic fluke
Fasciolopsis buski is important in some parts of Asia. The worm has a life cycle
that moves from man (or pig or dog) to snail to water plant and then to man again.
Animals or people become infected by eating the encysted metacercariae on water
plants, such as seed pods of water caltrop, bulbs of water chestnut, and roots of
lotus, water bamboo, etc. In cases where those diseases associated with
intermediate hosts in the pond are endemic and their respective hosts are present in
that area, waste recycling using aquatic plants is not advisable.
Aquatic vegetation enhances the production of mosquito by protecting the
larvae from wave action, providing a habitat for breeding and interfering with
mosquito control procedures. The two major vectors are Anopheles that transmits
malaria, and Mansonia that carries filariasis and encephalitis.
The eggs of Mansonia are laid on the undersides of leaves of aquatic weeds
just above the surface of the water. The mosquito larvae inserts it’s respiratory
siphon into the air-containing tissues of the plant and need not come to the
surface of water for air. The air is obtained from the submerged portions of the
plant, especially from the roots. Different Mansonia species have a preference