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Lead and its inorganic compounds

DESIGNATIONS

CAS No.: 7439-92-1
Registry name: Lead
Chemical name: Lead
Synonyms, Trade names: Plumbum
Chemical name (German): Blei
Chemical name (French): Plomb
Appearance: grey metal, bluish white shine on freshly cut surfaces

BASIC CHEMICAL AND PHYSICAL DATA

BASIC DATA OF SELECTED COMPOUNDS

ORIGIN AND USE

Usage:
In 1987, some 60 % of the lead produced was used to make batteries (ULLMANN, 1990). Further areas of application are lead pipes, alloys, cables, pigments and anti-knock agents in fuel. On average, 25 - 40 % of the lead used throughout the world is obtained by recycling scrap and lead waste (MERIAN, 1984).

Important lead compounds:

Origin/derivation:
Lead is an element forming approx. 0.002 % of the Earth's crust. The most important minerals are galena (PbS), cerussite (PbCO₃), crocoite (PbCrO₄) and pyromorphite (Pb₅(PO₄)₃Cl).

Production figures:
Lead production for most important lead producing and consuming countries, 1987:

(figures from ULLMANN, 1990)

Toxicity

Characteristic effects:

Humans/mammals: Lead can be absorbed by inhalation of dusts or by eating foods containing lead and - in the case of plants - by way of soluble lead salts in soils. Whereas inhalation is the major source of intake in workplace exposure, ingestion and resorption in the gastro-intestinal tract predominate in the population in general. It has recently become established that considerable quantities of lead enter the human body via drinking water (lead pipes).

Lead inhibits the various enzymes of the haemoglobin metabolism thus reducing the oxygen balance and the respiratory volume. Lead reduces the activity of the d -aminolaevulinic acid-dehydratase in the erythrocytes. Damage occurs with long-term intake of less than 1 mg/day. Symptoms of chronic poisoning are lead deposits along the edge of the gums as well as colic fits and spasms. Apathy, irritability, insomnia and - in some cases - behavioural irregularities in children are indications of damage to the nervous system. Lead passes through the placenta and accumulates in the foetus. In Germany, lead is listed in pregnancy group B (risk of embryonic damage is assumed).

The upper limit for the blood-lead level before it is considered to reach harmful proportions is 35 m g Pb/100 ml of blood for adults and 30 m g Pb/100 ml in children and pregnant women. The WHO applies a limit value of 100 µg Pb/100 ml of blood but is even considerably lower in most countries.

Inorganic lead compounds are resorbed in the gastro-intestinal tract. Children resorb lead more easily than adults (DVGW, 1985). Some 90 % of the resorbed lead is bonded to the erythrocytes and thus distributed throughout the entire body. It is deposited above all in the bones.

Approximately 90 % of the lead absorbed orally is excreted again; 75-80 % by elimination in the kidneys (MERIAN, 1984). A small quantity is deposited in hair and nails, exuded with sweat or stored in mother´s milk.

Plants: Plants mainly absorb lead from the soil, but only to a small extent from the atmosphere. Lead has a toxic effect on growth: application initially results in enhanced growth, but from a concentration of 5 ppm, this is counteracted by severe growth retardation, discoloration and morphological abnormalities (UBA, 1976). There is an adverse influence on photosynthesis, respiration and other metabolic processes. As a final step, lead inhibits the intake of essential nutrients from the soil. Pb⁺⁺ has only a slight effect on the growth of taller plants. Generally speaking, it is the quality rather than the yield which suffers. Compared to the toxicity in humans, the phytotoxicity of lead is of minor importance.

ENVIRONMENTAL BEHAVIOUR

Water:
Surface water forms an accumulation sink for lead compounds. Insoluble lead compounds sink and are adsorbed in the sediment or accumulate on suspended matter (in particular the clay fraction). Aquatic plants likewise accumulate lead. The biochemical oxidation of organic substances is inhibited at lead concentrations above 0.1 mg/l; fauna is depleted by concentrations above 0.2 mg/l and 0.3 mg/l is the threshold for fish toxicity (trout and white fish) [DVGW, 1985].

Groundwater is adversely affected by soluble lead compounds (e.g. lead chloride, nitrate). Nevertheless, it has been established that drinking water that passes through lead pipes may contain high lead concentrations (depending on the groundwater chemism). Lead is not chemically affected by deoxygenated water. In lead pipes, carbonated water forms lead carbonate deposits on the inner pipe surface.

Air:
Large quantities of lead are released into the atmosphere by combustion processes. There is a major difference between urban and rural areas. Lead compounds may be transported over a considerable distance depending on the speed and direction of the wind as well as precipitation and humidity. However, most of the lead in the atmosphere directly sediments or is removed by precipitation. Lead bonds to small dust particles in the air which in turn are deposited on vegetation and soil. Lead from motor-vehicle emissions accumulates in the immediate vicinity of roads.

Soil:
The absorption rate depends on the properties of the soil. There is a considerable affinity with humic substances. The pH is important for the availability of lead from its compounds. A low pH is linked to a high degree of desorption into the soil solution. However, as lead is quite immobile (e.g. more than cadmium), it remains in the topsoil and is not absorbed by plants to the same extent. Soils thus represent an important sink for lead compounds. Additional contamination results from the deposition of sewage sludge containing lead on farmland. Only extremely high contamination rates constitute a hazard to groundwater.

Half-life:
Lead remains in the atmosphere for roughly 7 - 30 days (FATHI & LORENZ, 1980). The biological half-life in blood is between 20 and 40 days; in bones up to several years (WHO, 1987).

Food chain:
Lead is found in all foodstuffs and fodders because it is ubiquitous. Vegetable foodstuffs generally contain more lead than animal products. This is the result of their special exposure: dust precipitations containing lead cling to the surface of plants and are thus consumed. In higher life forms, the maximum concentrations are found in internal organs such as the liver and kidneys. The increase in concentration is as follows in aquatic systems: water < fish prey < fish < sediment (DVGW, 1985).

Most humans absorb lead through their food (roughly 440 - 550 m g per day) and drinking water (some 20 m g per day) (DFG, 1982). At places where lead is produced or processed, atmospheric pollution is an additional problem. Approximately 30 - 50 % of the lead inhaled remains in the lungs (WHO, 1987); the rest is absorbed by the body and usually deposited in the bones.

ENVIRONMENTAL STANDARDS

Note:

¹⁾ The lead content of a sample taken from a lead pipe after draining off the water should not exceed 0.05 mg/l. If a water sample is taken directly or after the water has been allowed to flow off and if the lead content frequently or considerably exceeds 0.1 mg/l, remedial measures must be taken to reduce the risk of lead intake by consumers.
²⁾ Limit value for natural treatment
³⁾ Limit value for chemophysical treatment
⁴⁾ Mandatory value for simple and standard physical, chemical and refined chemical treatment and sterilisation
⁵⁾ Application of sewage sludge to soil used for agricultural or horticultural purposes prohibited (pollutant content of dry, mineral soils)
⁶⁾ Total tolerable content in cultivated soil
⁷⁾ Legally permitted additional annual loading of soil
⁸⁾ Pb and its compounds, stated as Pb
⁹⁾ Pb and its anorganic compounds as suspended dust, stated as Pb
¹⁰⁾ Pb and its anorganic compounds within dust sediments, stated as Pb
¹¹⁾ Exposure of pregnant women to lead can damage the embryo even when in compliance with MAK and BAT value.
¹²⁾ Parameter: lead
¹³⁾ Parameter: delta-aminolaevulinic acid

- The lead content of fuel is limited by law in numerous countries in an attempt to reduce the emissions from motor-vehicle traffic. The maximum level in petrol in the Federal Republic of Germany and Switzerland is 0.15 mg/l. More and more EC countries are starting to prescribe the use of unleaded fuel such as has been in force in several American states for many years.

- Certain industrial lead emissions are likewise subject to legislation. Thus, for example, the German TA-Luft (1986) fixed the IW1 immission values for lead as a constituent part of suspended dust at 2 m g/m³ to guard against health hazards and at 0.25 mg/(m²d) to minimise the nuisance level. Furthermore, the amount of inorganic lead dust with a mass flow of 25 g/h may not exceed 5 mg/m³. During the production of lead batteries the dust emissions must not exceed 0.5 mg/m³ at a mass flow of 5 g/h or more.

- The German Lead - Zinc Law (1974) stipulates that eating, drinking and cooking utensils may not give off lead after being boiled for 30 minutes with 4 % acetic acid.

- The 1977 Paint Law prohibits the use of lead in paints, foodstuffs, semi-luxury goods and consumer goods.

- The 1988 Order Governing the Use of Pesticides totally prohibits the use of lead compounds for such purposes.

- Usage banned in D in line with 1985 Order on Cosmetics

Comparison/reference values

Assessment/comments

Lead is not a physiologically essential element. It is most frequently absorbed in foodstuffs and at the workplace. The persistence of lead and its compounds has caused a ubiquitous distribution. Accumulation by way of food chains can thus hardly be prevented, but nevertheless, it can be largely minimised by way of local emission restrictions. Investigations in the field of toxicity in humans should be based on the blood-lead level of children and pregnant women.

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