Boron is used in fire retardants, as a component of enamels, in the photographic, cosmetic, leather, paint, textile and wood-processing industries. Borax, a major boron compound, is used as a cleaning compound and may occur in domestic and/or industrial effluents. Because of its wide variety of industrial uses, there are many potential pathways for entering the aquatic environment.

Boron is not commonly monitored for in UK marine waters. Grimwood and Dixon (1997) report some values for total boron at two sites in the North-East region of the Environment Agency (ranging from an annual average of 700 mg l^-1 to 4,627 mg l^-1).

Boron, with oxidation states of 0 and +3, may form various boranes (hydrides) and organoboron compounds. The environmental chemistry of boron in water is not well understood, but the predominant boron species in seawater is boric acid (76%) while the borate anion (B(OH)^-) accounts for approximately 13% (CCREM 1987).

An exhaustive literature review on the toxicity of boron to marine organisms has not been carried out for the purposes of this profile. The information provided in this section is taken from existing review documents (Mance et al 1988, and Grimwood and Dixon 1997). The most sensitive groups of organisms have been identified.

Mance et al (1988) reviewed the toxicity of boron to saltwater organisms. They found only limited data, which made it difficult to determine whether any group of organisms exhibited greater sensitivity. The authors proposed an EQS (for the protection of saltwater life) of 7,000 mg l^-1 (expressed as a total annual average concentration) which is currently adopted in UK legislation (HMSO 1989). Due to a lack of data, it was deemed that the derivation of an objective EQS was not possible. However, a tentative EQS of 7,000 mg l^-1 was derived by applying an arbitrary factor of 10 to the lowest, most reliable 96 hour LC50 of 74,000 mg l^-1, reported for the dab Limanda limanda. The derivation of a lower standard by using a larger safety factor was considered unnecessary as the tentative EQS is proposed at a level approximating normal ambient concentrations of boron in seawater. Nevertheless, it was recommended that the EQS should be reviewed once a larger dataset became available.

Grimwood and Dixon (1997) reviewed data on the saltwater toxicity of boron since the review by Mance et al. They found no reliable toxicity data that indicated higher sensitivity of saltwater organisms had been reported for boron. The authors recommended that the tentative EQS of 7,000 mg l^-1 (total annual average) proposed by Mance et al was probably appropriate for the protection of all saltwater life. However, the lack of toxicity data should be taken into account and this recommendation reviewed in the light of any new data.

There is some evidence that boron accumulates in marine zooplankton, algae and seaweeds, although tissue levels are generally low (BCF <50) (CCREM 1987).

Potential effects include:

• acute toxic effects to marine organisms at concentrations above the EQS of 7,000 mg l^-1 (annual average) in the water column;
• bioaccumulation in marine zooplankton and algae.

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