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Pollution may impair brain development worldwide, researchers say

Nov. 7, 2006
Courtesy Harvard School of Public Health 
and World Science staff

In­dus­tri­al pol­lu­tion may have ham­pered mil­lions of chil­dren’s brain de­vel­op­ment world­wide, a new study from the Har­vard School of Pub­lic Health and Mount Si­nai School of Med­i­cine claims.

Cour­te­sy Min­ne­so­ta Pol­lu­tion Con­t­rol Ag­en­cy
The re­search­ers said this “si­lent pan­demic” may have boost­ed the num­ber of re­tard­ed people while sapping the ranks of the in­tel­li­gent. And while steps have been taken to cur­tail the pol­lu­tion, more must be done, they ar­gued.

“The hu­man brain is a pre­cious and vul­ner­a­ble or­gan … even li­m­it­ed da­m­age may have se­ri­ous con­se­quences,” said Phi­l­ippe Grand­jean of the Har­vard School in Cam­b­ridge, Mass., the stu­dy’s lead au­thor.

Ev­i­dence accumulating over sev­er­al decades has linked many in­dus­tri­al chem­i­cals to ills in­clud­ing re­tar­da­tion, au­tism and short at­ten­tion spans, the sci­en­tists said, but past re­search has­n’t ad­e­quate­ly clar­i­fied the risks to chil­dren.

The stu­dy, an anal­y­sis of an ar­ray of past re­search, ap­pears on­line in the Nov. 8 is­sue of the med­i­cal jour­nal The Lan­cet. It ex­am­ines pub­lic da­ta on chem­i­cal tox­ic­i­ty and iden­ti­fies 202 chem­i­cals as harm­ful. 

The re­search­ers urged tough reg­u­la­tions to pro­tect chil­dren, some of which are al­ready in ef­fect the Eu­ro­pe­an Un­ion. Such rules would re­quire proof of chem­i­cals’ safe­ty be­fore their use, as op­posed to most cur­rent reg­u­la­tions, which re­quire proof of tox­ic­i­ty be­fore a chem­i­cal is re­strict­ed.

A de­vel­op­ing brain is much more vul­ner­a­ble than an adult brain, the re­search­ers said: it un­der­goes a tre­men­dous­ly com­plex se­ries of pro­cesses, any dis­rup­tion of which can have per­ma­nent con­se­quenc­es. The vul­ner­a­bil­ity, they added, lasts from fe­tal de­vel­op­ment through ad­o­les­cence. 

Grandjean and co-au­thor Phil­ip J. Lan­dri­gan of the Mount Si­nai School in New York com­piled a list of 202 pol­lu­t­ants known to be brain-tox­ic, based on sources in­clud­ing the U.S. Na­tion­al Li­brary of Med­i­cine’s Haz­ard­ous Sub­stances Da­ta Bank.

They then scanned pub­lished lit­er­a­ture on five sub­stances of part­i­cu­lar­ly well-doc­u­mented tox­ic­i­ty. They found a si­m­i­lar pat­tern: first, re­search­ers rec­og­nize tox­ic­i­ty to adults, and episodes of poi­son­ing among chil­dren; next, ep­i­de­mi­o­lo­gi­c­al ev­i­dence shows that ex­po­sure to low­er lev­els causes neu­robe­hav­ioral deficits in youth.

Lead was the first such sub­stance iden­ti­fied, though its tox­ic­i­ty to adult brains had been known for cen­turies, ac­cord­ing to the re­search­ers. They ar­gued that vir­tu­al­ly every­one born in in­dus­tri­al coun­tries be­tween 1960 and 1980 was ex­posed to lead from pet­rol. This may have halved the num­ber of IQ scores above 130, con­sid­ered su­pe­ri­or in­tel­li­gence, while in­creas­ing the num­ber of peo­ple scor­ing less than 70, con­sid­ered men­tal­ly re­tard­ed. While na­tions have taken major steps to re­duce lead ex­po­sure, the same isn’t true of many other substances. 

“Even if sub­stan­tial doc­u­men­ta­tion on their tox­ic­i­ty is avail­a­ble, most chem­i­cals are not reg­u­lat­ed to pro­tect the de­vel­op­ing brain,” said Grand­jean. “Only a few sub­stances, such as lead and mer­cu­ry, are con­trolled with the pur­pose of pro­tecting chil­dren. The 200 oth­er chem­i­cals that are known to be tox­ic to the hu­man brain are not reg­u­lat­ed to pre­vent ad­verse ef­fects on the fe­tus or a small child.”

To­day, lead poi­son­ing in U.S. chil­dren is es­ti­mat­ed to cost the econ­o­my $43 bil­lion an­nu­al­ly; methylmer­cu­ry tox­ic­i­ty, $8.7 bil­lion, Grand­jean said, but these may be se­vere un­der­es­ti­mates.

“Other harm­ful con­se­quenc­es from lead ex­po­sure in­clude short­ened at­ten­tion spans, slowed mo­tor co­or­di­na­tion and height­ened ag­gres­sive­ness, which can lead to prob­lems in school and di­min­ished eco­nom­ic pro­duc­tiv­i­ty as an adult,” Lan­dri­gan said. “The con­se­quenc­es of child­hood neurotox­icant ex­po­sure lat­er in life may in­clude in­creased risk of Parkin­son’s dis­ease and oth­er neu­ro­gen­er­a­tive dis­eases.”

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Industrial pollution may have hampered millions of children’s brain development of worldwide, according to new study from the Harvard School of Public Health and the Mount Sinai School of Medicine. The researchers called the findings evidence of a “silent pandemic” that may have reduced the number of intelligent people while boosting the ranks of the retarded. “The human brain is a precious and vulnerable organ… even limited damage may have serious consequences,” said Philippe Grandjean of the Harvard School in Cambridge, Mass., lead author of the study. For instance, the researchers said virtually all children born in industrialized countries between 1960 and 1980 were exposed to lead from petrol. This may have halved the number of IQ scores above 130, considered superior intelligence, they argued, while increasing the number of people scoring less than 70, considered mentally retarded. Evidence building up over several decades has shown that many industrial chemicals can lead to ailments including retardation, autism and short attention spans, the scientists said, but past research hasn’t adequately clarified the risks to children. The study, an analysis of an array of past research, appears online in the Nov. 8 issue of the medical journal The Lancet. It examined public data on chemical toxicity and identified 202 chemicals as harmful. The researchers urged tough regulations to protect children, some of which are already in effect the European Union, that would require proof of chemicals’ safety before their use. Current regulations tend to work the opposite way, requiring proof of toxicity before a chemical is restricted. A developing brain is much more vulnerable than an adult brain, the researchers noted, and undergoes a tremendously complex series of processes; any disruption of these can have permanent consequences. The vulnerability, he added, lasts from fetal development through adolescence, Grandjean said. He and co-author Philip J. Landrigan of the Mount Sinai School in New York compiled a list of 202 environmental chemicals known to be brain-toxic, based on sources including the U.S. National Library of Medicine’s Hazardous Substances Data Bank. They then scanned published literature on five substances for which toxicity was particularly well documented. They found a similar pattern: first, researchers recognize toxicity to adults, and episodes of poisoning among children. Next, a epidemiological evidence shows that exposure to lower levels causes neurobehavioral deficits in youth. Lead was the first such substance identified, though its toxicity to adult brains had been known for centuries, according to the researchers. “Even if substantial documentation on their toxicity is available, most chemicals are not regulated to protect the developing brain,” said Grandjean. “Only a few substances, such as lead and mercury, are controlled with the purpose of protecting children. The 200 other chemicals that are known to be toxic to the human brain are not regulated to prevent adverse effects on the fetus or a small child.” Today, lead poisoning in U.S. children is estimated to cost the economy $43 billion annually, and methylmercury toxicity, $8.7 billion annually, Grandjean said, but these may be severe underestimates. “Other harmful consequences from lead exposure include shortened attention spans, slowed motor coordination and heightened aggressiveness, which can lead to problems in school and diminished economic productivity as an adult,” Landrigan said. “The consequences of childhood neurotoxicant exposure later in life may include increased risk of Parkinson’s disease and other neurogenerative diseases.”