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Cadmium pigments no hazard in molding.

A recent scientific study by researchers at GE Plastics' Mt. Vernon, Ind., R&D laboratory found no detectable amounts of air-borne cadmium emitted during injection molding of cadmium-pigmented engineering plastics.

GE initiated the research after a new OSHA standard (29 CFR 1910.1027) was published last year, which established a lower permissible exposure limit (PEL) for cadmium fumes and dust of 5 micrograms/|m.sup.3~) of air (8-hr time-weighted average), with an "action level" of 2.5 |microg~g/|m.sup.3~. OSHA typically sets an action level below the PEL as a level that triggers various regulatory responsibilities on the part of an employer, such as regular workplace monitoring.

Although cadmium is known to be toxic in some forms, pigment manufacturers have long maintained that calcined cadmium pigments, which are produced at temperatures above 1200 F, are insoluble and therefore biologically inert. OSHA, however, made no exception for cadmium pigments in writing the standard.

'WORST-CASE' SIMULATION

GE researchers Jose V. Bonilla and Randy A. Milbrath conducted experiments to see what effect, if any, the new standard would have on molders of plastics containing cadmium pigments. Cadmium-pigmented samples of GE engineering resins (polycarbonate, PBT, ABS, PPO alloy, and polyetherimide) were injection molded on a 500-ton press. Cadmium pigment loadings were relatively high for these resins--1.43-1.82%. Each resin was dried for 4 hr before molding and was molded at its upper recommended processing temperature--conditions that the researchers term "slightly abusive."

Bonilla and Milbrath sampled the air within 2 to 6 in. above the injection machine nozzle, mold vents, and a 10-lb purging (drool) from the nozzle, as well as 3 ft from the machine in a typical operator location. These samples represented "worst-case scenarios for potential cadmium emissions--start-up and purging," the authors say. Four shots were molded of each resin, and the air above the drools was sampled for 1 hr at a sample flow rate of 2 liters/min. Total volumes of air collected were 120 liters for the drools and 312-388 liters for all other samples.

'NON-DETECTABLE'

The samples were analyzed by an OSHA-approved method using an inductively coupled plasma atomic-emission spectrophometer. Calibration tests showed that at the volumes of air collected, GE's analytical procedure would detect cadmium down to a detection limit of 0.27-0.40 |micro~g/|m.sup.3~ for the molding air samples and 0.83-1.0 |micro~g/|m.sup.3~ for the drool air samples--well below the action level. GE's tests found no detectable cadmium in all air samples for all resins.

The authors caution that their study did not cover the potential for inhaling cadmium-containing dust resulting from secondary operations such as sanding, sawing, and regrinding. They advise that "standard industrial hygiene practices that include engineering controls and work practices should routinely be used to minimize the potential for exposures to cadmium by these operating conditions."
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Copyright 1993, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Naitove, Matthew H.
Publication:Plastics Technology
Date:Nov 1, 1993
Words:477
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