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Herbicides
and Pesticides
The 1993 World Health Organisation
guideline values for drinking water lists
a whole series of pesticides with maximum
permissable limits in drinking water.
The number of different
pesticides available and the amount used in
improving agricultural yields have significantly
increased over the past 40 years.
It is known that most surface
derived and ground waters contain some pesticide
residues in the range of 0.001 to 0.1 µg/l
(µg/l = microgrammes per litre). These
concentrations are very small and result from
the legitimate use in the community.
The analysis for these pollutants
is very expensive due to the highly technical
equipment necessary.
The current standards are:
Individual
substances 0.1 µg/l
Total substances 0.5
µg/l
These values were chosen
mainly on the limits of detection of the analytical
equipment than on any known information on
toxicity to human beings.
‘Safe’ herbicides
and pesticides are mainly so called because
of their very short active life once exposed
to the atmosphere or day/sunlight, they degrade
very quickly. However if they are degraded
by natural ultraviolet light, after they enter
the ground they do not degrade and eventually
are deposited in underground water - aquifers
and reservoirs. They have been found in deep
borehole waters.
To be safe, there are barriers/reduction/adsorption
materials commonly available and an adsorption
column is recommended to be included in any
private supply system.
The adsorption material
is usually contained in a disposable or refillable
cartridge fitted inside a small filter housing,
which becomes an integral part of a private
supply system.
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