21/02/2008

Health-based recommended occupational exposure limit for Kaolin

The Health Council of the Netherlands recommended late last year health-based
occupational exposure limits for Kaolin dust.

Limit values

In the Netherlands, there is no occupational exposure limit for respirable
kaolin dust. The UK Health and Safety Executive (HSE) and the American
Conference of Governmental Industrial Hygienists (ACGIH) recommend 2 mg/m3
respirable kaolin dust as the occupational exposure limit. The ACGIH threshold
limit value (TLV) of 2 mg/m3 respirable kaolin dust is only valid if it
contains less than 1% quartz and no asbestos. In addition, the ACGIH has
notified kaolin as an A4 substance, meaning that kaolin is not classifiable as
a human carcinogen. The US NIOSH recommends a 10h-TWA exposure limit of 5 mg/m3
and the US OSHA uses an 8h-TWA exposure limit of 5 mg/m3.

Kinetics

No adequate studies on the kinetics and the mechanisms of action of kaolin are
available.

Effects

Many reports of well-studied cases and a number of cross-sectional studies,
mainly in the United Kingdom and the USA, have shown that long-term exposure to
kaolin may lead to pneumoconiosis, which has been named kaolinosis.
Pneumoconiosis is diagnosed by chest X-ray, and is categorized as simple
pneumoconiosis (category 1-3) or complicated pneumoconiosis (category A-C)
(annex D). Clinical symptoms and effects on pulmonary function are mainly
observed in the complicated form. Although the mildest form of pneumoconiosis
ILO category 1 is not yet associated with a decrease of pulmonary function, the
committee considers pneumoconiosis category 1 as an undesired health effect, in
agreement with the European Committee's report on miner's pneumoconiosis. In
this report, pneumoconiosis category 1 is recognized as an occupational disease.
Studies with exposure data or dose-effect relationships are scarce. The
available animal data are not suitable for the derivation of a health-based
recommended occupational exposure limit. Adequate studies on the
carcinogenicity or reproduction toxicity of kaolin are not available.
There is one study with human data in which a dose-response relationship was
reported for respirable kaolin dust. According to this study, the average
non-smoking worker reaches pneumoconiosis ILO category 1 at the age of 60 after
40 years of occupational exposure to 2.1 mg/m3 respirable kaolin dust. From the
data as presented in this publication, the committee can not establish a NOAEL
or LOAEL. The publication does not contain information on the quartz content of
the respirable dust exposures, the presence of which in kaolin can make it
difficult to distinguish kaolinosis from silicosis (pneumoconiosis caused by
quartz).

Evaluation and advice

According to the committee, it has convincingly been shown that occupational
exposure to kaolin has adverse health effects involving the lungs and with
pneumoconiosis as the clinical finding.

It is the committee's opinion that occupational exposure to 2.1 mg/m3
respirable kaolin dust is undesired as it constitutes an substantial risk for
the development of pneumoconiosis ILO category 1. However, no studies are
available from which the committee can establish a NOAEL or LOAEL for kaolin
dust. Therefore, the committee cannot derive a health-based recommended
occupational exposure limit for kaolin dust.

In this advice, the committee gives an additional consideration on the
inhalatory exposure to respirable kaolin dust in the workplace.

More info


AplusA-online.de - Source: Health Council of the Netherlands