Further considerations of the skeletal system as a biomarker of episodic chlorpyrifos exposure

The mummichog, Fundulus heteroclitus, is a common inhabitant of eastern seaboard estuaries. As such, it can be affected by coastal agricultural and other nonpoint source runoff. We examined the effects of short-term episodic exposures to an agricultural pesticide, chlorpyrifos, on brain acetylcholinesterase (AChE) activity and vertebral yield strength in lab-reared and wild-caught fish. Brain AChE activity was chosen as an indicator because it is the target system for organophosphate action. Vertebral yield strength was chosen as an indicator because previous research warranted further investigation (Karen et al., 1998). Four daily or weekly 6 h exposures (2.5, 5.0, and 10.0 microg/l chlorpyrifos) in decreased salinity seawater (5 g/kg) significantly reduced brain AChE activity. The lowest concentration was within the range of reported environmental chlorpyrifos concentrations; thus inhibition of brain AChE from environmental chlorpyrifos exposures may pose a hazard to estuarine organisms. Yield strength measured in lab-reared fish appeared to be more sensitive to episodic chlorpyrifos exposures, because chlorpyrifos was a significant factor in 75% (3 out of 4) of tests performed with lab-reared fish. Chlorpyrifos exposure was a significant factor in only 25% (1 out of 4) tests performed with wild fish. These results suggested that changes in the responses of bone to load testing, following several short exposures to an organophosphate, could be sensitive indicators in lab-reared organisms.