A computer-controlled whole-body inhalation exposure system for the oil dispersant COREXIT EC9500A

Abstract

An automated whole-body inhalation exposure system capable of exposing 12 individually housed rats was designed to examine the potential adverse health effects of the oil dispersant COREXIT EC9500A, used extensively during the Deepwater Horizon oil spill. A computer-controlled syringe pump injected the COREXIT EC9500A into an atomizer where droplets and vapor were formed and mixed with diluent air. The aerosolized COREXIT EC9500A was passed into a customized exposure chamber where a calibrated light-scattering instrument estimated the real-time particle mass concentration of the aerosol in the chamber. Software feedback loops controlled the chamber aerosol concentration and pressure throughout each exposure. The particle size distribution of the dispersant aerosol was measured and shown to have a count median aerodynamic diameter of 285 nm with a geometric standard deviation of 1.7. The total chamber concentration (particulate + vapor) was determined using a modification of the acidified methylene blue spectrophotometric assay for anionic surfactants. Tests were conducted to show the effectiveness of closed loop control of chamber concentration and to verify chamber concentration homogeneity. Five automated 5-h animal exposures were performed that produced controlled and consistent COREXIT EC9500A concentrations (27.1 ± 2.9 mg/m(3), mean ± SD).

FIGURE 1

Block diagram of the inhalation exposure system used to expose rats to COREXIT EC9500A.

FIGURE 2

Picture of the inhalation exposure system used to expose rats to COREXIT EC9500A.

FIGURE 3

Illustration of the custom exposure chamber (Cube 150) that housed the rats during inhalation exposures to COREXIT EC9500A.

FIGURE 4

“Main” tab of the software graphical user interface used to acquire, record, and control system parameters during an inhalation exposure.

FIGURE 5

Results of chamber aerosol concentration homogeneity: (A) cage number positions within the exposure chamber and (B) the normalized average concentrations from gravimetric filter samples from four test runs. Data are shown for each cage and the reference sample that pulled COREXIT EC9500A aerosol from directly above the center of the cage rack. Error bars represent standard errors.

FIGURE 6

Particle size distribution of the aerosol (in terms of counts) in the breathing zone of the rats during the COREXIT EC9500A inhalation exposures as measured with an aerodynamic particle sizer (APS) and a scanning mobility particle sizer (SMPS). The dark line on the graph represents a lognormal distribution with a count median aerodynamic diameter of 285 nm and geometric standard deviation of 1.7.

FIGURE 7

Example of the real-time particulate concentration during a COREXIT EC9500A inhalation exposure. The syringe flow, which is regulated by the feedback loop that controls the concentration, is also shown and multiplied by 10 for display purposes. SS Mean and STD refer to the steady state mean and standard deviation of the concentration. The SS is defined as the concentration values between when the concentration reaches 90% of its target value and when the syringe pump is turned off at the 5-h point in the exposure.

FIGURE 8

Real-time particulate concentrations during the 5-h COREXIT EC9500A inhalation exposures (where feedback was utilized, illustrated with the lighter lines), along with a test run initiated without feedback control (indicated with the dark line). Notice that a much more consistent concentration throughout each exposure is achieved with the addition of feedback control.