Lead (Pb) and some of its chemical compounds are virtually ubiquitous in the environment. Lead can be found in air, drinking water, as well as in soil and various food items. The possibility of lead exposure in human is therefore of great significance from health point of view. Lead does not spare any organ in the body and is not known to serve any necessary biological function.

Unique Properties of Lead

• Lead is not bio-degradable

• It never disappears, only accumulates where it is deposited

• Lead provides no known biological benefits to humans

• Young children absorb lead more rapidly than adults.

• More than 95% of the retained lead is accumulated in bones, where it is in continuous exchange with soft tissue pools.

• The half - life of circulating lead in blood is about one month

As the levels of blood lead increase, their effects become more pronounced. Lead levels of more than 50 µg/dl manifest clinically, with life threatening complications occurring at levels of 100 - 150 µg/dl. At levels < 50 µg/dl, sub-clinical effects occur. Most important of these 'low level effects' is impaired cognitive performance and behavioural changes. Intelligence Quotient (IQ) increments are associated with increasing blood lead levels, a relationship that is clear above 10 µg/dl. Individual blood lead levels may also vary with age and season. In certain population, where there is significant exposure of children to house dust and soil contaminated with lead,there has been an increase in blood.

Table 8 Clinical Symptoms Versus Blood Lead Levels In School Children of Delhi

Clinical Symptoms	Blood Lead Levels
	< 20 µg/dl (n=96)	20-39 µg/dl (n=38)	40 µg/dl (n=46)
Growth Failure	1	-	1
Hyper Activity	-	-	-
Hearing Loss	2	-	2
Pallor	8	3	2
Pica	15	11	10
Acute Encephalopathy	-	-	-
Abdominal Colic	42	16	16
Anorexia	14	6	6
Sporadic Vomiting	3	2	3
Constipation	2	-	-
Seizures	1	-	-
Pigment lines on gums	19	4	6
Asymptomatic	28	10	16

n = number of subject examined.

Source: Veena Kalra, AIIMS, 1998

lead levels with age beginning at infants (< 1 year) upto a peak of 2 years of age. This pattern is apparently related to age related changes in mouthing behaviour and mortality.

Lead has effects on many biochemical processes in particular, effects on haem synthesis have been studied extensively in both adults and children. The effects of lead on hemopoietic system result in decreased hemoglobin synthesis and anemia in children at blood lead concentrations above 40 µg/dl. For neurological, metabolic and behavioural reasons, children are more vulnerable to the effects of lead than adults. The most substantial evidence from studies of population with blood lead levels generally below 25 µg/dl relates to decrements in intelligence quotient (IQ). The size of the apparent IQ effect, as assessed at 4 years and above, is a deficit between 0 and 5 points for each 10 µg/dl increment in blood lead level. In a survey conducted by AIIMS, Delhi on school children of Delhi, it was observed that the IQ levels of children with low blood lead was higher as compared to those having high blood lead (Table 9).

Table 9 Intelligence Quotient (IQ) Vs Blood Lead Levels in School Children of Delhi

Intelligence Quotient (IQ)	Blood Lead Levels
	< 20 µg/dl	20-39 µg/dl	> 40 µg/dl	Total
69 & below	-	-	-	-
70-79 (Borderline)	9 (36%)	8 (32%)	8 (32%)	25
80-89 (Normal)	44 (55%)	18 (22.5%)	18 (22.5%)	80
90-109 (Average)	24 (58%)	3 (12%)	12 (30%)	41
110-119 (Above average)	3 (100%)	-		3
Total	80	31	38	149

Source: Veena Kalra,AIIMS New Delhi

An association between blood lead level and hypertension (blood pressure) has been reported. The likely order of magnitude is that for any two fold increase in blood lead level (i.e. 17 µg/dl - 34 µg/dl), there is a mean 1 mm Hg increase in systolic blood pressure. The association with diastolic pressure is of a similar but smaller magnitude. A major contributory factor to the exacerbations of lead toxicity is iron deficiency anemia. In the tropical countries, iron deficiency anemia is a major health hazard among children caused by a deficiency in dietary intake.

In India, the use of cosmetics containing lead is a major source of exposure; in Mexico, it is widespread use of lead for glazing pottery used to hold food and water. In Egypt, lead solder used in the grinding stone of flour mills was recently found to cause alarming levels of lead poisoning.

Lead Levels In School Children Of Delhi

Blood samples were collected by AIIMS, New Delhi from 200 school children from Sirifort and Daryaganj areas of Delhi during 1997. The blood lead levels were categorised into five classes based on the blood lead levels as defined by Centre for Disease Control (CDC), Atlanta. It was observed that the blood lead levels among 56 % of the school going children in Sirifort area and 72% in Daryaganj had elevated blood lead levels (Table 10).

Table 10 Blood Lead Levels Among School Children Of Delhi

Source: Veena Kalra,AIIMS New Delhi

The Government has taken steps to reduce the ambient air lead concentration of Delhi by phasing out leaded petrol (0.56 gm Pb/lit) and introducing unleaded petrol (0.013gm Pb/lit) from September, 1998. This step has resulted in substantial reduction of lead in the atmosphere of Delhi (Figure 8). Lead phase out programme from petrol/gasoline is given in Table 11

Table 11 Gasoline Lead Phase Out Program In India

Phase	Implementation Date	Gasoline Lead Content	Areas Covered
Phase-I	June,1994	Low leaded (0.15g/l)	Delhi, Mumbai, Calcutta and Chennai
Phase-II	1.4.1995	Unleaded (0.013g/l)	Delhi, Mumbai, Calcutta and Chennai
Phase-III	1.1.1997	Low leaded (0.15g/l)	Entire Country
Phase-IV	1.9.1998	Unleaded (0.013g/l)	NCT-Delhi and 45 other cities
Phase-V	31.12.1998 (Advanced to 1.9.1998)	Unleaded (0.013g/l)	All capitals of states/UTs and other major cities
Phase-VI	1.1.1999	Unleaded (0.013g/l)	National Capital Region
Phase-VII	1.2.2000	Unleaded (0.013g/l)	Entire Country

Note: Gasoline Lead content prior to June,1994=0.56g/L

Source: Air Quality status and trends, CPCB Report NAAQMS/14/2000-2001