Food / Health Breath of fresh air or lot of old lead?

Press, 9 May 1981, Page 10

Food / Health Breath of fresh air or lot of old lead?

Editorials in the weekly “British Medical Journal” reflect international concern about our exposure to lead. In a rare, signed-editorial, Daphne Gloag recently drew

attention to the increasing amounts of lead in our environment. Lead is added to most petrols and is emitted from car exhausts as a gas. The air breathed by urbanised societies contains measurable lead concentrations in most cities. Last year a study in “Science” showed 500 times more lead in the skeletons of present-day Americans than was found in Peruvians who died about 100 A.D. N.Z. environment In New Zealand most older houses were painted with lead-based paints. Children playing around verandahs and in the dust close to such old houses may absorb more lead. Vegetables and berry fruits grown close to such houses contain more lead. Riccarton Road in Christchurch is one busy urban highway with relatively high dust and air lead levels. Carcases of sheep which have grazed alongside congested main roads show much more lead than do other sheep. We may also absorb lead from canned foods and some water. Lead in humans The brain and nervous system, kidneys and the bone marrow, or the blood forming organ can be damaged by excess absorption of lead. Lead is both inhaled from the air and absorbed from food and water. It is then carried around in the circulation or blood stream by the red blood cells. It passes out through the kidney filters but, when present in excess, it can also be soaked up into the skeleton and bone marrow. This is. a protective mechanism for removing dangerous excesses on a temporary basis. Such excesses would normally be released when levels fell in the blood. Thus, the amount of lead in skeletons and teeth gives an effective general measure of long-term excessive exposure to lead. Lead and intelligence Newborn experimental rats are given lead in amounts which give blood levels of lead the same as those found in children living alongside roadways. All newborn mammals have a fast growth rate of the. developing brain, and definite biochemical damage from lead can be shown in the rat brain tissues. Although drawing conclusions from animal experiments is difficult, the best brain development in young • children with such blood levels may be at risk. Adults only absorb five to 10 per cent of any lead in the

food and water they consume. But human infants can absorb up to 50 per cent. Calcium deficiency leads to more lead absorption. This is of special concern inChristchurch because of the city’s mineral-deficient water. Voung infants in New Zealand may be at higher risk for slight brain damage as shortages of iron, copper, zinc and selenium worsen lead dangers. A high-fat diet, dangerously common in New Zealand, also increases absorption. Young New Zealanders living in any alluvial or volcanic areas would seem to be particularly vulnerable because all the contributing factors are stacked against them. What evidence exists that minor changes in intelligence are caused by undetected, mild lead toxicity? Few good studies have been carried out internationally — none in New Zealand of good design because money spent here on medical research is appallingly little. Studies of school children Bostom school teachers and parents independently filled in wide-ranging questionnaires for a study about the health and activities of the children in their classes. Teeth subsequently extracted from these children were analysed for lead content. This was done by a separate group of chemists who did not know from which children the numbered teeth. had come. Children with high lead content in the dentine of the teeth had been independently rated adversely for attention span, verbal and listening processes in the classroom. Poor organising ability in the children was also related to higher lead levels.

Electrical brain-wave recordings were also carried out. When abnormal changes

in these were combined with the poor results of psychology testing, the group of children with highest lead were found. This study led to much controversy. There, as here, official opinion was that parents would become alarmed. As a result of intervention by environmental impact groups, serious, high-level and informed debate took place with plans being made to phase lead out of petrol in many American states. Daphne Gloag notes the point made and not disputed that .a fall in IQ of only five points for the population of children as a whole would mean a doubling of the numbers of mentally retarded children with an IQ of under 70. Nutrition, food, and lead In a study published last year by doctors at the Environmental Health Department, Birmingham, England, it was shown that the preschool children with high lead levels were mainly Asiatics. It was concluded that the high blood lead levels were related to food rather than environmental factors such as lead in the air. This suggests a real need for an urgent review of the nutrition of Polynesians living in urban areas with low mineral water. We have too few trained research workers to carry out such prospective child health studies in New Zealand. So we must leave open the question of any burden of reduced intelligence carried by our community. At present, we just cannot be sure.