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Survey on Lead Free Solder Systems
Appendix 2: Toxicological evaluation of soldiers and fluxes
8 The toxicology of metals
Lead (Pb)
Tin (Sn)
Silver (Ag)
Copper (Cu)
Summary - toxicology
The absorption of lead by adults is relatively poorly from the gastro-intestinal tract
(10 %), whereas children absorb 40-50 %. No data were available about uptake through the
skin. Inhaled lead particles may be swallowed and subsequently absorbed from the
gastro-intestinal tract. The percentage of particles retained in the lung increases with
reduction in particle size. About 90 % of lead particles in ambient air that are deposited
in lungs are small enough (less than 0.5 mm) to be retained in
the alveols. Absorption of retained lead through alveoli is relatively efficient and
complete (9). Lead occurs in blood rich soft tissue (blood,
lungs, spleen, kidneys, liver and bone marrow) and skeleton. The half-life time of lead
concentration in soft tissue is approximately 40 days, whereas the lead bound in the
skeleton is halved in approximately 20 years. Lead ions is excreted in the faeces via the
bile and the urine (14).
Acute lead poisoning is relatively infrequent and occurs from ingestion of acid soluble
lead compounds or inhalation of lead vapours (14). Lead
causes depression of the central nervous system with symptoms like headache, restlessness,
changed behaviour, and decreased memory functions. The peripheral nervous system is also
affected, the symptoms being numbness of fingers and toes, and weakness of wrists and
ankles. Lead inhibits the haeme synthesis, i.e. the production of haemoglobin and
may cause anaemia. Humans exposed to lead have shown chromosomal aberrations in a number
of cytogenetic studies, but not in other studies. The evidence for lead being carcinogenic
is ambiguous. Lead impairs reproductive ability in both women and men. Lead also may cause
preterm delivery of babies and minor malformations.
The aquatoxicity of lead depends on the water hardness. The biocompatibility of lead is
smaller in hard water than in soft water. Lead is toxic to aquatic organisms. The
bioaccumulation is low.
Tin is poorly absorbed into the body from the gastro-intestinal tract. No data were
available about uptake through the skin or by inhalation. The highest tissue
concentrations in humans were found in the gastro-intestinal tract, bones, kidneys and the
liver. Minor concentrations were found in the lungs and adrenal glands. Tin ions is
primarily excreted in the urine and to a lesser extent in the faeces via the bile.
The acute toxicity of tin is low. Rare cases of tin allergy have been seen. Long-term
inhalation of tin and insoluble tin compounds may cause tin dust lungs (stannosis). Intake
of tin has caused vomiting, diarrhoea, and depression of the central nervous system with
symptoms like fatigue, headache and ataxia. Long-term intake of soluble tin salts has
caused liver and kidney toxicity. Tin is not toxic to reproduction, mutagenic or
carcinogenic.
Silver may be taken up from the gastro-intestinal tract and the lungs. Some silver
compounds may be absorbed through the skin. Silver binds to plasma proteins in the blood.
Silver is primarily accumulated in the pancreas, liver and spleen, and to a lesser extent
in other tissues. Silver is mainly excreted in the faeces via the bile. Urinary may take
place, when the blood level of silver is above a certain concentration.
Metallic silver is highly inert and is generally considered of low toxicity to
mammalian species including man. However, death has been observed in rats following
ingestion of large doses colloidal silver (15). In rare
cases, silver has resulted in skin allergy. Inhalation of high concentrations of silver
fume resulted in headache and dyspnoea, and later reduced oxygen pressure in capillary
blood. For many years, it was believed that the only effect from silver was argyria.
Argyria results after long-term exposure and is a cosmetic illness. Recent studies show,
that silver may be toxic to the kidneys. In animal studies, silver was able to pass the
blood-brain barrier and accumulate in certain areas of the brain. Such animals were less
active than unexposed animals, which may indicate that silver may have a harmful effects
on the central nervous system. Silver is not mutagenic or carcinogenic. There is some
evidence that silver may cause minor developmental anomalies in the foetus.
Silver ions are lethal to bacteria, and are very toxic aquatic organisms. Algae,
daphnia, fresh water mussels, and fathead minnows were all found capable of accumulating
silver; but the food chain was not an important route of silver accumulation for animals
at higher tropic levels, suggesting no food chain magnification.
Copper is an essential metal in humans, animals and plants. Copper is taken up from the
gastro-intestinal tract and the lungs, and is primarily accumulated (stored) in the liver
and to some extent in the kidneys. Copper is excreted in the faeces via the bile. To a
some extent, the body is capable of regulating the copper accumulation in the liver.
Copper is a rare skin sensitiser. Acute copper poisoning by ingestion causes
gastro-intestinal symptoms like gastric pain, nausea, vomiting and diarrhoea. Severe
poisoning may cause kidney and liver failure, and possibly haemolytic anaemia.
Chronic copper poisoning in humans is not known except in Wilson’s disease.
Patients with this disease suffer from disorders in the copper metabolism and have an
abnormal accumulation of copper in the liver (30 times over normal level) and the brain,
possibly resulting in cellular necrosis and liver cirrhosis, and neurological symptoms. In
normal persons, ingested copper is mainly accumulated in the liver and only reaching e.g.
the brain in low doses. This is confirmed by animal studies.
Copper is not affecting reproduction. Copper is not carcinogenic, but is mutagenic in
some bacterial strains.
Copper is toxic to aquatic organisms, bacteria, and algae. The toxicity to fish is
comparable to that of lead.
Toxicological profiles for lead, tin, silver and copper was compiled to give basis for
comparing the toxicities of these metals to humans and environment. The table below shows
a brief conclusion of the profiles.