Revisiting the Safety of Pesticides: A Closer Look at Neurodevelopment

[Guest guest]

http://ehp.niehs.nih.gov/members/2005/7940/7940.html

http://ehp.niehs.nih.gov/members/2005/7940/7940.pdf

*

A Case for Revisiting the Safety of Pesticides: A Closer Look at

Neurodevelopment

Theo Colborn

Environ Health Perspect 114:10-17 (2006).

University of Florida, Gainesville, Florida, USA; TEDX (The Endocrine

Disruption Exchange) Inc., Paonia, Colorado, USA

Address correspondence to T. Colborn, PO Box 1253, Paonia, CO 81428,

USA. Telephone: .

E-mail: colborn@...

* Introduction

* Evidence of Exposure to Pesticides

* Human Epidemiology

* A Case Study: The Cryptic Neurodevelopmental Effects of CPF

* Other Pesticide Products That Interfere with Neurodevelopment

* Discussion

Abstract:

The quality and quantity of the data about the risk posed to humans by

individual pesticides vary considerably. Unlike obvious birth defects,

most developmental effects cannot be seen at birth or even later in

life. Instead, brain and nervous system disturbances are expressed in

terms of how an individual behaves and functions, which can vary

considerably from birth through adulthood. In this article I challenge

the protective value of current pesticide risk assessment strategies in

light of the vast numbers of pesticides on the market and the vast

number of possible target tissues and end points that often differ

depending upon timing of exposure. Using the insecticide chlorpyrifos as

a model, I reinforce the need for a new approach to determine the safety

of all pesticide classes. Because of the uncertainty that will continue

to exist about the safety of pesticides, it is apparent that a new

regulatory approach to protect human health is needed.

[from the discussion:]

In a recent study, Bowers et al. (2004) found a different profile of

developmental neurotoxicity between polychlorinated biphenyls (PCBs;

such as Aroclor 1254) alone and with a mixture of organochlorine

pesticides. Very low doses of the chemicals together delayed ear

opening, affected geotaxis, and reduced grip strength. Ultimately,

mortality, growth, thyroid function, and neurobehavioral development

were affected. It is safe to say that there are very few people in the

developed world today who are not carrying PCBs in their bodies. If

animal testing continues to be used for determining the safety of

pesticides, at least one group of the test animals should be exposed to

PCBs before testing the pesticides for their ability to cause

unpredictable interactive effects such as those described above.

It should be pointed out that the same signaling systems (AC cAMP)

involved in the sex-selective changes in brain development have also

been shown to alter heart and liver function in adulthood (Meyer et al.

2004a, 2004b). The AC system is ubiquitous throughout the body. In the

future, the most efficient, comprehensive assays will take advantage of

the fact that most chemicals have more than one effect in one system.

Cross-disciplinary teams will be required to design these assays so that

every organ system is carefully screened for damage. And most important,

this will reduce by thousands the numbers of animals needed for testing.

However, improved neurodevelopmental tests with laboratory animals will

not fulfill their greatest potential if they are not backed up by better

batteries of tests to detect functional disabilities in children. Such

new, sophisticated quantitative tests are now available and are being

updated regularly. These tests go beyond diagnostic testing to

" performance evaluation " and are designed to detect the subtle effects

of chronic, low-dose exposure (son et al. 2000).

In conclusion, an entirely new approach to determine the safety of

pesticides is needed. It is evident that contemporary acute and chronic

toxicity studies are not protective of future generations. The range of

doses used in future studies must be more realistic, based on levels

found in the environment and human tissue. In this new approach,

functional neurologic and behavioral end points should have high

priority, as well as the results published in the open literature. In

every instance, the impacts of transgenerational exposure on all organ

systems must be meticulously inventoried through two generations on all

contemporary-use pesticides and new pesticide coming on the market. To

protect human health, however, a new regulatory approach is also needed

that takes into consideration this vast new knowledge about the

neurodevelopmental effects of pesticides, not allowing the uncertainty

that accompanies scientific research to serve as an impediment to

protective actions....