Download 12.78 Malathion - World Health Organization

GUIDELINES FOR DRINKING-WATER QUALITY
in 1989 but using a compound intake estimate considered to be more appropriate in
light of additional data and recognizing that there may be substantial exposure to
lindane from its use in public health and as a wood preservative.
Assessment date
The risk assessment was conducted in 2003.
Principal references
FAO/WHO (2002) Pesticide residues in food – 2002. Rome, Food and Agriculture Organization of the United Nations, Joint FAO/WHO Meeting on Pesticide Residues
(FAO Plant Production and Protection Paper 172).
WHO (2003) Lindane in drinking-water. Background document for preparation of
WHO Guidelines for drinking-water quality. Geneva, World Health Organization
(WHO/SDE/WSH/03.04/102).
12.78 Malathion
Malathion (CAS No. 121-75-5) is commonly used to control mosquitos and a variety
of insects that attack fruits, vegetables, landscaping plants and shrubs. It can also be
found in other pesticide products used indoors, on pets to control ticks and insects
and to control human head and body lice. Under least favourable conditions (i.e.,
low pH and little organic content), malathion may persist in water with a half-life of
months or even years. However, under most conditions, the half-life appears to be
roughly 7–14 days. Malathion has been detected in surface water and drinking-water
at concentrations below 2 mg/litre.
Malathion inhibits cholinesterase activity in mice, rats and human volunteers. It
increased the incidence of liver adenomas in mice when administered in the diet. Most
of the evidence indicates that malathion is not genotoxic, although some studies indicate that it can produce chromosomal aberrations and sister chromatid exchange in
vitro. JMPR has concluded that malathion is not genotoxic.
A health-based value of 0.9 mg/litre can be calculated for malathion based on an
allocation of 10% of the JMPR ADI – based on a NOAEL of 29 mg/kg of body weight
per day in a 2-year study of toxicity and carcinogenicity in rats, using an uncertainty
factor of 100 and supported by a NOAEL of 25 mg/kg of body weight per day in a
developmental toxicity study in rabbits – to drinking-water. However, intake of
malathion from all sources is generally low and well below the ADI. As the chemical
occurs in drinking-water at concentrations much lower than the health-based value,
the presence of malathion in drinking-water under usual conditions is unlikely to represent a hazard to human health. For this reason, it is considered unnecessary to derive
a guideline value for malathion in drinking-water.
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12. CHEMICAL FACT SHEETS
History of guideline development
The 1958 and 1963 WHO International Standards for Drinking-water did not refer to
malathion, but the 1971 International Standards suggested that pesticide residues that
may occur in community water supplies make only a minimal contribution to the
total daily intake of pesticides for the population served. Malathion was not evaluated
in the first edition of the Guidelines for Drinking-water Quality, published in 1984, in
the second edition, published in 1993, or in the addendum to the second edition, published in 1998.
Assessment date
The risk assessment was conducted in 2003.
Principal references
FAO/WHO (1998) Pesticide residues in food – 1997 evaluations. Part II – Toxicological
and environmental. Geneva, World Health Organization, Joint FAO/WHO Meeting
on Pesticide Residues (WHO/PCS/98.6).
WHO (2003) Malathion in drinking-water. Background document for preparation of
WHO Guidelines for drinking-water quality. Geneva, World Health Organization
(WHO/SDE/WSH/03.04/103).
12.79 Manganese
Manganese is one of the most abundant metals in the Earth’s crust, usually occurring
with iron. It is used principally in the manufacture of iron and steel alloys, as an
oxidant for cleaning, bleaching and disinfection as potassium permanganate and as
an ingredient in various products. More recently, it has been used in an organic compound, MMT, as an octane enhancer in petrol in North America. Manganese greensands are used in some locations for potable water treatment. Manganese is an
essential element for humans and other animals and occurs naturally in many food
sources. The most important oxidative states for the environment and biology are
Mn2+, Mn4+ and Mn7+. Manganese is naturally occurring in many surface water and
groundwater sources, particularly in anaerobic or low oxidation conditions, and this
is the most important source for drinking-water. The greatest exposure to manganese
is usually from food.
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