US Agency Releases Draft Toxicological Profiles

The US Agency for Toxic Substances and Disease Registry (ATSDR) has released draft toxicological profiles for four substances for public comment.

These are:

> antimony;

> molybdenum;

> SILICA; and

> 2,4-D (2,4-dichlorophenoxyacetic acid).

The ATSDR is congressionally mandated to develop toxicology profiles for hazardous substances, found at National Priorities List (NPL) sites. Each peer-reviewed document draws from available literature on the substance’s properties to characterise the toxicologic and adverse health effects of analysed substances.

Antimony

Antimony, when mixed into an alloy, is used in lead storage batteries, solder, sheet and pipe metal, bearings, castings and pewter.

The draft profile indicates that the metal can cause heart problems and lung effects in workers, including lung cancer. The International Agency for Research on Cancer (Iarc) has determined antimony trioxide as a group 2B substance (possibly carcinogenic) and antimony trisulfide as group 3 (not classifiable).

The Occupational Safety and Health Administration (Osha) has set a limit of 0.5 mg/cubic meter for antimony in workroom air. The EPA has determined that exposure to drinking water of 0.01 mg/L is not expected to cause health effects for one to ten day exposures; the corresponding lifetime exposure level is 0.006 mg/L.

Molybdenum

According to the draft profile, an intake of 45 μg/day of the element molybdenum is recommended for adults. However, exposure to high levels can be harmful.

Concerns from long-term exposure to dust in the air include damage to the nasal cavity, epiglottis and lungs. Studies suggest that ingesting very large volumes can damage reproductive systems and may cause kidney and liver damage.

The National Institute for Occupational Safety and Health (Niosh) has established a level of 5,000 mg/cubic meter for insoluble compounds and 1,000 mg/cubic meter for soluble compounds that it considers "immediately dangerous and likely to cause death or immediate or delayed permanent adverse health effects".

Molybdenum is principally found as an oxide or sulfide compound, and is widely used to make steel alloys.

Silica

Silica is a naturally occurring compound that comes in many forms. Silica sand and gravel are used for building and construction, hydraulic fracturing, ceramics and abrasives. Crystal quartz forms of silica are used in jewellery, electronics, and the optical component industry.

Health effects from certain silica forms are found in workers exposed for long periods of time, or from extremely heavy exposure over a short period of time (acute silicosis).

The draft assessment says that the greatest risks to human health from exposure to crystalline silica include silicosis and lung cancer. The Department of Energy (DOE), Niosh and Osha have all set limits for exposure in occupational settings.

2,4-D

2,4-D is the active ingredient in many herbicide products. Although animal studies have indicated a number of effects – including liver and kidney effects, decreased breast milk production and blood alteration – the ATSDR says harmful effects are not likely to be experienced when manufacturer’s instructions are followed.

Comments on the four draft profiles will be accepted until 11 September.