Pesticides in drinking water--a case study.

Pesticides occupy a unique position among chemicals found in drinking water, since they are deliberately used to control pests in agriculture and public health. They comprise a variety of compounds of various chemical properties (many of which being persistent in the environment), toxic potential, and mechanism of action. Safety assessment for drinking water is conducted by allocating health-based guidelines for exposure through this environmental medium. The tolerable daily intake (TDI) approach is used by WHO in the case of pesticides with assumed thresholds of effect, while low-dose extrapolation is used in the case of non-threshold carcinogens. Risk management, however, can also be based on the precautionary principle. Risk assessment evaluates the risk emanating from a given exposure on the basis of all available data.

Dietary intake, levels in food and estimated intake of lead, cadmium, and mercury.

Since 1980, systematic efforts have been made by the Joint UNEP/FAO/WHO Food Contamination Monitoring Programme to collect information on dietary intake of various contaminants, exemplified by lead, cadmium and mercury. In 1980-88, average adult intakes of lead varied from 1 to 63 micrograms/kg bw/week, approaching or exceeding the Provisional Tolerate Weekly Intake (PTWI) of 25 micrograms/kg bw in four countries providing data. Major sources in food and drinking water differed from country to country. A downward trend was observed consequent on reduction in use of lead-soldered cans and of lead in petrol. Few countries provided data on intakes by infants and children (more vulnerable groups) but the mean exceeded the PTWI in three countries, heavily influenced by levels in water and lowest in infants consuming only breast milk. Average adult intakes of cadmium were, with one exception, below the PTWI of 7 micrograms/kg bw; intakes by children were higher on a body weight basis but still within the PTWI in countries supplying data. Highest levels occurred in offal (mean 320 micrograms/kg) and shellfish (200 micrograms/kg) but, because of amounts consumed, reduction of concentrations in cereals, roots and tubers would be most effective. Important sources of contamination included phosphate fertilizer sewage sludge, plated/galvanized equipment, enamels and glazes. For mercury, average intakes were below the PTWI (300 micrograms/person; 200 micrograms/person or 3.3 micrograms/kg bw as methylmercury) for adults and for breast-fed infants. Contributions from fish varied from 20 to 85%; in some countries because of different dietary habits, cereals or meat may contribute similar amounts. Because of inadequate data on food other than fish, intake estimates are biassed and sometimes based solely on typical levels in fish.

Key elements of food contamination monitoring programmes.

The key elements of programmes for monitoring food contamination are reviewed in relation to their purposes, scope and priorities. Attention is drawn to the requirements and quality assurance of procedures for sampling and analysis, and methods of handling and processing analytical surveillance data. The benefits to be derived from national monitoring programmes are improved food safety, warning of problems of contamination, provision of intake data for evaluation of health hazards, better management and use of natural resources, supply of data on environmental pollution and reliable information on food safety for the public, and provision of a means of checking the effectiveness of regulatory mechanisms and planning technological developments.

Revision of the WHO guidelines for drinking water quality.

This paper describes the activity of the World Health Organization in the field of drinking water quality, particularly the revision of the Guidelines for drinking water quality published in 1984. This process will be completed with the publication of new guidelines in 1993. The paper reports the physical, chemical and biological agents considered in the revision process, the procedure used to define the new guidelines, their meaning and their relationships with statutory limits.

Dietary intake of pesticide residues: cadmium, mercury, and lead.

Information on the dietary intake of chemical contaminants has been obtained from institutions participating in GEMS/Food. Contaminants studied include certain organochlorine and organophosphorous pesticides, PCBs, cadmium, mercury, and lead. The intakes are compared with toxicologically acceptable intake levels established by international expert groups. In most cases, dietary intakes of organochlorine and organophosphorous pesticides are well below the Acceptable Daily Intake (ADI) of the respective pesticide. Of some 21 countries providing information on the average dietary intake of cadmium, only in one case is the Provisional Tolerable Weekly Intake (PTWI) exceeded. Several countries identified cereals and cereal products and root and tuber vegetables as the main contributors to the dietary intake of cadmium. For mercury, all reported intakes are below the PTWI of methylmercury. The contribution of fish to the total intake of mercury varied from 20% to 85%, depending on the country. Therefore, the general assumption that fish is the main contributor to the total dietary intake of mercury may, at times, not be justified. Average dietary intake of lead exceeding or approaching the PTWI are reported for adults and infants and children in some countries. Foodstuffs which contribute most to the intake of lead vary from country to country, and have been identified as being alternately drinking water, beverages, cereals, vegetables and fruit.