In England and Wales, water companies have
nearly completed a major investment programme affecting many of their water
treatment works and costing over £1,000 million (US$ 1.6 billion). In addition
there may be running costs of about £50 million per year.
The investment programme was instigated to ensure compliance
with the pesticide parameter, which requires that water supplied by the company
to their customers at the point of supply does not exceed 0.1µg/l (parts per
billion) of individual pesticides at any time. This standard is set out in the
Water Supply (Water Quality) Regulations 1989 which transposed the requirements
of the EC Drinking Water Directive into national legislation.
The Director General of Water Services has a duty to ensure
that the water companies can finance the provision of water which meets all the
required quality standards and customers are paying for this work in their water
bills. By the end of the pesticide compliance programme, customers will be
paying on average £4-5 each year to finance the building and operation of water
treatment plants to reduce the level of pesticides found in drinking water.
These are high technology plants which are expensive to build and to operate.
For example, some processes used employ ozone, which is generated using
electrical discharge, and the regeneration of the Granular Activated Carbon used
to adsorb pesticides is expensive. Both procedures are energy-intensive.
The drinking water standard
In 1980, the Drinking Water Directive set the
concentration of pesticides in drinking water at a maximum of 0.1µg/l, at this
time, a surrogate zero level. The analytical techniques were at a relatively
early stage of development, as was the examination of medical and toxicological
information. The precautionary principle was therefore applied to the setting of
the standards, until appropriate evidence was available, the permitted level of
pesticides being set at this very low level. Taken in isolation, this standard
is having a significant impact on bills, it is not a cost-neutral option.
Inconsistency
Furthermore, the application of the precautionary
principle is not consistent. While the precautionary principle is applied to
drinking water standards, agrochemicals continue to be used. The principle has
not been applied to all areas of human exposure. For example, much higher
pesticide levels are permitted in fruit and vegetables and it is likely that a
mixture of pesticides, residues and metabolites will be ingested.
In England and Wales, some foods are permitted to contain up
to 5mg/kg (parts per million) of some pesticides. It is acceptable for potatoes
to contain 3mg/kg of carbendazim and yet the water supplied to cook them is not
permitted to contain more that 0.1µg/l of the same pesticide, a standard 30,000
times stricter.
Similarly, some shampoos prescribed for medical purposes and
in skin contact contain 0.5g or 1g/100ml of pesticide, yet the equivalent of
0.25g in an Olympic sized swimming pool would fail the pesticide standard for
drinking water. It is now worth considering whether to adopt an integrated
approach in dealing with human exposure to pesticides?
The term pesticides is a wide one, describing the compounds
used rather than any linkage in their mode of action or toxicity to humans. This
can give rise to apparent anomalies. Trichloroacetic acid (TCA) comes under the
general term pesticides and is regulated by the standards, although it can be
produced as a by-product of the water treatment process rather than entering the
water supply as a pesticide. Other compounds such as dieldrin and aldrin are
likely to give rise to more concern.
Toxicity based standards
There is a considerable database on toxicity and
associated information on a number of the compounds loosely grouped as
pesticides. The data is now available to comment on individual compounds. The
latest edition of the World Health Organisation (WHO) Guidelines for Drinking
Water Quality (1993) has put forward guideline values for 34 pesticides. These
guideline values represent the concentration of a constituent that does not
result in any significant risk to the health of the consumer over a lifetime of
consumption. The WHO set out a range of guidelines for pesticides from below 0.1µg/l
to 100µg/l. This information is sufficiently soundly based to use as the basis
for setting individual standards for those pesticides with guideline levels. It
is no longer appropriate to continue to apply the precautionary principle.
However, the proposed revision of the EC Drinking Water Directive does not
revise the pesticide standard in line with WHO advice.
The adherence to the 0.1µg/l standard is having a direct
impact on water bills each year. Although the introduction of treatment plant to
reduce pesticide levels has had other effects on the quality of water produced,
such as changing the taste and odour, these have not generally been required
legally. The need to build the treatment plants, some to very tight timetables,
has been the adherence to the precautionary principle. It could well be that
there has not been a significant reduction in the risks to human health. The
proposed revision to the Drinking Water Directive proposes the introduction of
standards for by-products from the very treatment processes that are being used
to reduce pesticide use. There is concern that some of these by-products may be
genotoxic carcinogens. Dealing with a perceived risk may be increasing real
risks to consumers.
Does the polluter pay?
The enforcement of the pesticide standard at 0.1µg/l
requires companies and hence the customer to pay for a reduction in the levels
of pesticides. The principle of 'the polluter pays' has yet to be applied to the
contamination of water resources by pesticides or indeed nitrates. This means
that customers are paying both for the removal of contaminants from drinking
water, where they are not the polluter, and for the purification of their waste,
where they are the polluter, to meet other requirements, for example, the Urban
Waste Water Treatment Directive. This anomaly has a significant impact on
customers' bills.
If there was consistency in the application of standards in
an integrated way across the environment much of this expenditure may not be
needed. For example, if the current standard is to be upheld in drinking water,
the logical conclusion would be for these standards and associated principles to
be maintained throughout the environment, both ground water and surface waters
being protected from pollution by pesticides. Alternatively, it may be decided
that the WHO Guideline levels, based on toxicological assessments of individual
members of this heterogeneous group of compounds, could be applied. The new EC
Framework Directive on European Community Water Policy due to be published later
this year is expected to address the quality of ground water and surface water.
However, with the current hybrid approach the burden of paying for the removal
of pesticides from drinking water falls to the customers.
Only a small proportion of the 20 million kg of pesticide
active ingredients used in the UK each year enters water sources. However, when
the compliance programme is finished, it will cost over £100 million per year
to finance and operate, about £5 for each kilogram of pesticide used. This is a
substantial cross-subsidy from the customer to the polluter.
Ofwat places much emphasis on the principle that the polluter
should pay. We believe that the optimum approach is to control the use of
pesticides, so that water supplies can comply with all the requirements relating
to pesticide levels in drinking water. These sources could then provide a
wholesome supply of drinking water without sophisticated and expensive pesticide
removal treatment processes.
Rowena Tye works for the Costs and
Performance Division of Ofwat (which regulates the water industry in England and
Wales). The views expressed are those of the author and do not necessarily
reflect the views or policy of Ofwat, or any other government department.
[This
article first appeared in Pesticides News No. 35,
March 1997, page 18]