Lead is widely distributed all over the world in the form of its sulfide, the ore galena. Lead ranks about 36th in natural abundance among elements in the earth's crust. Ores of secondary importance are cerussite and anglesite. Maltese rock formations are markedly deficient in lead ores, the mineral being found only in minute traces in the local limestones. Lead has been important for industrial purposes since ancient times. The metal was imported to Malta by the Bronze Age people with pieces of lead being excavated from Borg in-Nadur and Tarxien Cremation Cemetry. The Romans in Malta similarly imported the element and used it for making water pipes, soldered with an alloy of lead and tin. Other Roman uses of the metal included household articles such as leadened buckets, and the stock and collar of ship anchors. The high carbonate content of natural water in Malta usually forms a coating on lead pipes inhibiting the formation of soluble lead hydroxide. It is thus unlikely that the use of lead water conduits during Roman times predisposed significantly to lead intoxication. The use of lead-based utensils for cooking food may however assist the contamination of foodstuff. In 1904 a case of suspected poisoning reported to the Police was traced to the intake of a considerable quantity of lead being absorbed from the broken enamel of some of the pans used as cooking utensils.

By the nineteenth century, the toxic effects of lead salts were recognised by medical practitioners. The Maltese medical journal Il-Barth , published by Dr. G. Guilia, on a number of occasions drew the attention of the medical profession to the various ways in which lead intoxication could occur. Thus in 1876 attention was drawn to the possiblity of chronic poisoning from lead-contaminated beer, and from lead contained in cosmetics, water pipes and infant feeding bottles. The formation of a dark blue line on the gums was associated by Maltese medical practitioners with the use as an astringent mouth gargle of lead acetate or sugar of lead in 1842. They did not however recognise this as a sign of lead toxicity. Lead acetate is a white crystalline soluble salt with a very sweet taste. A judicial postmortem was performed in 1861 on a man suspected of having died from the effects of chronic poisoning by lead acetate. Chemical analysis of portions of the viscera were also performed, but no traces of lead could be discovered. At least two two deaths from lead intoxication were reported in the fortnightly mortality reports of the late nineteenth century (1-15 February 1885 and 16-22 February 1891). These were probably occupational deaths. Both occurred in male individuals aged 25-45 years from Cospicua.

Other sources of lead salts in the Maltese diet were subsequently identified. In May 1897, samples of raw coffee imported from Trieste were noted to have a suspicious appearance in that the berries were dark, greenish and soiled the hands when handled. These were analysed by the Department of Health Laboratory who found these to be coated with a mixture of finely powdered plumbago (graphite) and lead chromate. Later on during the same year, another quality of coloured coffee was detected, the berries being yellowish in colour. Analysis showed these to be coloured with lead chromate. The percentage of this colouring material differed with the different samples being generally less than 0.0525 grams of chromate per 100 gms berries, though a number of berries were dotted all over with the bright yellow lead salt. Of 370 samples of coffee taken from different shops, not less than 261 were found to be coloured with lead chromate. The coffee originated from Trieste, Genoa, Hamburg and London. On the 7 June 1897, a law prohibiting the importation of coffee coloured with substances injurious to health was enacted. In the subsequent six months, only 3.7% of tested coffee samples were found to be contaminated with lead chromate. Lead chromate, or chrome yellow (PbCrO4), a crystalline powder used as a yellow pigment, is prepared by the reaction of lead acetate and potassium bichromate. Chrome red, orange chrome yellow, and lemon chrome yellow are some of the pigments obtained from lead chromate.

Another instance of contamination of foodstuff with lead occurred in 1908. At this time the number of factories manufacturing of "aerated waters" had greatly increased owing to the cheapness of the machinery. Abour 12% of the samples tested by the Public Health Laboratory were found to be unsuitable for consumption because of the presence of a consideranle amount of lead, which was traced to the use of impure tartaric and citric acid used in the manufacture.In May 1903 an epidemic of lead posoning was reported in Maltese bakers. On enquiry this was traced to the use of wood as fuel obtained from the thickly painted timber from HMS Hibernia. The famous Base Flagship HMS Hibernia had been launched in 1804 and broken down in 1902. The amount of leaded paint used in her maintainance over a hundred years can only be left to the imagination. A general inspection of all the bakeries in Malta showed that wherever such fuel was in use, symptoms of lead poisoning became evident. Lead was also discovered in the bread supplied to the public when baked in ovens heated with lead painted fuel. 166 samples of ashes from ovens and 72 samples of bread were analysed. Fifty-seven percent of the ash samples contained lead oxide in a proportion varying from traces to 8.6%, while 50% of bread samples contained lead. All symptomes of lead poisoning disappeared when energetic measures were taken to prevent the use of this wood as fuel, especially since those mainly effected were the bakers themselves. Red lead or minium (Pb3O4), a scarlet, crystalline powder formed by oxidizing lead monoxide, is the pigment in paint used as a protective coating for wood, iron and steel. Even though the sale and use of Red Lead paint is now controlled, this paint remains an important source of lead in the Maltese ecosystem through the burning or scraping of old wooden items previously treated with Red Lead paint.

The twentieth century saw a dramatic increase in the number of petrol-driven vehicles. These vehicles have contributed significantly towards the introduction of lead in the Maltese ecosystem. Lead tetraethyl or the bromide is the chief constituent of the antiknock compound added to gasoline to prevent premature detonation in internal-combustion engines; it is considered a significant contributor to air pollution. The significant presence of lead contamination from vehicular emmisions in Malta was demonstrated in a Junior College (Royal University of Malta) exhibition in 1971. Sample leaves collected from the main street in Floriana (Malta) were washed with concentrated acid. After filtration of the carbon particlres and adjustment of the acidity, the solution was tested with potassium chromate and shown to have a high proportion of lead in solution. The significance of the high levels of lead in the Maltese ecosystem was finally confirmed in 1981. The Maltese population was shown to have a high level of exposure to lead and cadmium when compared to other countries. A population survey showed that the Maltese population had a significantly higher mean blood lead levels than the Belgian population. The mean lead level in Malta was 307 ug/l with a maximum value of 863 ug/l, while in Belgium the mean level ranged 145-240 ug/l with maximum values of 279-570 ug/l depending on the locality studied. Among Britain's children the average quantity of lead in the blood is between 70-75 ug/l. The US Centres for Disease Control (CDC) considers any value above 100 ug/l as an unsafe level. The blood lead levels in Malta were similar in both men and women suggesting that this was not an occupational hazard but a continuous enviornmental one. A follow-up study two years later reported a slight drop in the mean blood lead levels, but was still elevated at 243 ug Pb/l. Subsequent studies have persistently confirmed the high lead levels in the various sections of the Maltese population including children and neonates. Other studies have shown that blood lead levels are elevated in Maltese children aged 7-9 years with a mean of 241.5 ug Pb/l in Malta and 194.4 ug Pb/l in Gozo. The latter island has a more rural environment promoting a lower traffic density, thus accounting for the lower blood lead levels observed. The blood lead levels in the rural community seem higher than would be expected from petrol lead exposure alone, thus suggesting that the source of lead in the enviornment is multifactorial and not simply due to traffic emissions.

Lead compounds derived from vehicular emissions are mostly inorganic and consequently exist in a particulate form. Lead, in the form of tetra-methyl lead or tetra-ethyl lead, is added to petrol to increase its octane rating to reduce engine knocking. Ethylene dibromide and ethylene dichloride are further added to petrol to remove the lead from the engine cylinders. The predominant lead product exhausted from automobiles is lead halides, which undergo chemical changes quite rapidly with other exhaust gases and in the atmosphere. Vehicular lead sources may enter the human organism through inhalation and/or ingestion. Inhaled lead is taken up more efficiently than through ingestion. The uptake of lead by inhalation is dependent on the lead concentration in the air, particle size and the breathing and ventilation rates. In the situation of air lead levels of 1 ug/m3 described for the Maltese ecosystem, an adult is estimated to take 15 ug Pb/day of which 50% would be deposited in the lungs. Ninety per cent of the deposited lead is absorbed and equilibrates between the circulation and the tissues. In the Maltese circumstances therefore, an adult living in areas of traffic congestion would absorb about 7.5 ug Pb/day of which 3.75 ug Pb/day remains in the circulation. Absorption of lead through the gastrointestinal tract is a relatively inefficient process. A number of conditions influence the rate of absorption of lead, particularly the chemical form in which it is ingested, the type of diet, and the individual's physiology. It has been estimated that the absorption of lead from the gastrointestinal tract into the bloodstream averages 10% in adults and 40% in infants. Vehicular lead emissions are sparingly soluble in water, but have been found to be 90% soluble in hydrochloric acid at a pH 1, stimulating the chemical conditions inside the stomach. The soluble lead forms are more efficiently absorbed by the gastrointestinal tract. Dust ingestion seems to be an unlikely pathway in adults. It has however been shown to be a significant source in children. Investigations have revealed that dust may account for half the total daily intake of lead by a young child amounting to an average value of 50-100 ug Pb/day. Dust can be ingested indirectly by eating sweets or sucking toys while playing at home or in the street. The child can transfer up to 50 mg of dust from his hands to a sweet after 30 minutes activity in a playground. A local study has demonstrated the high lead levels in dust from playgrounds in high traffic density areas and the relationship to dust lead levels to child hand-wipe lead levels. The risks of lead intake through ingestion of dust extends also in the home since housedust in urban areas has also been shown to have significantly higher lead levels when compared to rural areas. The increased transfer of lead from household, street and playground dust in areas of high traffic density has been demonstrated by the higher blood lead levels noted in children living in Malta compared to those living on the more rural island.

While vehicular emissions contribute substantially to the lead levels in soil, which levels are inversely proportional to the distance from the road; the organic matter in soil together with the high alkalinity of maltese calcareous soils immobilizes the lead decreasing its availability to plants. Thus fruit and vegetables, provided they are well washed from adhering soil and dust, are unlikely to be direct sources of lead ingestion. On the other hand, seafood may be an important source of ingestion of vehicular-originating lead in the Maltese circumstances. The level of lead in sea sediments in the vicinity of the capital city was found at 118 ug/g to be markedly higher to levels of other Mediterranean inshore sediment exposed to urban and industrial pollution (Thermaikos Gulf: 71 ug/g; Gulf of Venice: 45 ug/g). Certain edible shellfish, such as the Date Mussel and the Warty Venus, collected from Maltese waters have also been found to carry high lead levels. The main source of this high sediment lead is most likely to be car traffic rain washoff . Used car engine oil can also contribute either when disposed off in fields through leaching to soil and the water-table, or when sold to bakeries to be used as fuel. Another possible source of lead in the Maltese ecosystem may be the lead shot used by hunters which deposits onto the soil and slowly but gradually leaches into the soil and is absorbed by plants. This is a slow process which may be accelerated by the use of pesticides. While the use of leaded paint has now been controlled, some cheap imported toys may still use these types of paint. The burning of old wood which may have been painted in the past by "Red Lead" paint may also be contributory to chronic lead intoxication. Cases of lead intoxication were recently reported in Maltese drug users after heroin sold in the streets was laced with lead acetate.Vehicular emission is a definite contributor of lead in the Maltese environment resulting in the reported high blood lead levels of this population. Serious efforts to reduce the amount of leadened petrol and promote lead-free petrol must be taken by the authorities. There is evidence that the environmental benefits of lead-free petrol are being increasingly appreciated by the Maltese, resulting in an increase in lead-free petrol demands from 5281 m3 in 1992 to 10242 in 1994. In spite of this 94% increase in lead-free petrol demands, the leadened petrol at 63647 m3 in 1994 remains the major source of automobile fuel demanded. The authorities, alerted to the high blood levels in the Maltese population in the 1980s, instituted a number of community preventive measures to attempt control this environmental problem. It appears that these measures have had a significant favourable effect. A recent study has confirmed that there has been a definite lowering in PbB levels in newborns in 1996 when compared to a similar study conducted in 1985. While in 1985, 31.6% of neonates had PbB levels greater than 200 ug/l, no neonates studies in 1996 had these high values. However a high proportion of neonates in 1996 still had values for which the CDC recommends community prevention activities (>100 ug/l).