Introduction
- Lead occurs in the environment both naturally and, to a greater extent, from human activities such as mining and smelting, battery manufacturing and the use of leaded petrol (gasoline).
- Lead can also be present in food. Lead present in air may deposit on leafy vegetables. Aquatic food animals may also accumulate lead from contaminated waters and sediments. Although lead exists in both organic and inorganic forms, only inorganic lead has been detected in food.
- Lead can enter the human body via ingestion, inhalation and skin absorption. People involved in occupations such as painting and decorating, plumbing, construction work, and car repair are exposed to higher levels of lead from their work environment. Tobacco smoke is also a source of exposure to lead. Young children frequently put their fingers and other objects into their mouths, and thus are more prone to ingestion of lead paint chips and house dust or soil that may contain lead particles.
Toxicity of lead
- Lead has no essential function in human. Short term exposure to high levels of lead can cause abdominal pain, vomiting and anaemia. Chronic exposure of lead in children can lead to neurological impairment and reduction of intelligence quotient (IQ).
- For adults, chronic exposure to lead, which when accumulated in large amounts in the body, may result in anaemia, increased blood pressure and kidney damage.
- In 2006, the International Agency for Research on Cancer (IARC) classified inorganic lead compounds as probably carcinogenic to humans (Group 2A) on the basis of sufficient evidence of carcinogenicity in experimental animals and limited evidence in humans.
Safety Reference Value
- In 2010, JECFA withdrew the provisional tolerable weekly intake (PTWI) of 25µg/kg bw/ week established in 1999 for lead as it could no longer be considered health protective. JECFA opined that, health impact (calculated to be associated with a population increase in systolic blood pressure of 1 mmHg) for adult is considered negligible when the exposure level is lower than 1.2 µg/kg bw/day. General speaking, it is best for everybody to keep their exposure to lead, from all sources (drinking, eating, inhaling), as low as possible.
Local studies
According to the First Hong Kong Total Diet Study Report No. 5 on Metallic Contaminants published by the Centre for Food Safety (CFS) in January 2013, dietary exposures to lead in average and high consumers of the population were 0.21 μg/kg bw/day and 0.38 μg/kg bw/day, respectively. The estimated dietary exposures to lead were below the level of 1.2 μg/kg bw/day considered by JECFA to have a low risk of increasing the systolic blood pressure in adults. The main dietary source of lead was "vegetables and their products" which contributed to 30% of the total exposure. Other major sources were "non-alcoholic beverage", "mixed dishes" and "cereals and their products" which contributed to 16%, 14% and 13% of the total exposure, respectively The food subgroup "water" only contributed to 2.5% of the daily exposure to lead among average consumers.
Advice to the Public
- Because of the ubiquitous nature of lead in the modern industrial world, low levels of lead exposure may be unavoidable.
- Maintain a balanced and varied diet so as to avoid excessive exposure to lead from a small range of food items.
- Soak and wash vegetables, particularly leafy vegetables, thoroughly in water before cooking as this can remove a significant portion of lead-contaminated dust and soil that may have been deposited on the surfaces of the vegetables.
Advice to the Trade
- Observe good agricultural and manufacturing practices to minimise lead contamination in food.