Boron

Endpoint summary

Description of key information

Sources and selection/screening of ecotoxicological data

The ecotoxicological data in this report are derived from original papers on the subject, gathered from the industry and environmental agencies, or published in international journals, and covered studies that focussed on common ecotoxicological parameters such as survival, growth and/or reproduction. All data are screened for their relevancy and reliability. Relevance concerns the appropriateness of the data for a particular hazard identification or risk characterization, while reliability is based on the inherent quality of the test method and report. Reliability is addressed through Klimisch criteria. Only the toxicity data that received a Klimisch score of 1 or 2 and that were considered relevant were used to derive the HC5,50 value, and robust summaries are included in the IUCLID database. Toxicity data that received a Klimisch score of 3 or 4 are not discussed in this document without a specific need.

Determination of whether a specific study was relevant for the environmental effects assessment of boron was based on species (standard/non-standard species), route of exposure/application, test concentrations, test substance and test duration (acute/chronic).

Reliability assessment of a study was based on factors such as GLP-compliance, description of the applicable test methods, chemical analysis of exposure concentrations, observed concentration-response relationship, test acceptability and validity criteria and finally, proper statistical endpoint derivation.

 

It should be noted that the potential essential effects of boron have been studied on a variety of freshwater fish, amphibians, invertebrates and plants. At lower concentrations, boron has been found to be beneficial to some freshwater organisms. Boron, for instance, is essential for nitrogen fixation in some species of algae (Smyth and Dugger, 1981), fungi and bacteria (Saiki et al., 1993; Fernandez et al., 1984), some diatoms and algae and macrophytes (Eisler, 2000). Required levels may vary, especially among plants, such that essential levels for one species may be toxic to another (Eisler, 1990). Fort et al. (1999) found that boron was nutritionally essential for reproduction and development in frogs (Xenopus laevis). Rowe et al. (1998) found that the shape of the dose-response curve in rainbow trout (Oncorhynchus mykiss) and zebrafish follows the U-shaped adverse response of an essential nutrient. For both species inceasd mortality of embryos and zygotes are reported below specific B-threshold levels.

Boron does not appear to be essential for all species, however. Evaluation of essentiality in some animals is limited by the innate boron content in plant-based animal feeds.

 

More detailed information on each of the mentioned relevancy/reliability criteria is provided in the Background Document “Environmental effects assessment of boron”, which is attached in the technical dossier in IUCLID Section 13.

 

 

Summary of relevant acute ecotoxicity data:

Relevant information on standard fish species, invertebrates and algae was retained for classification purposes when tests were in line with accepted standard testing guidelines. An overview of the crital data is geven hereunder: 

For fish, a reliable data point for boron, added to the test medium as boric acid, was a 96h-LC50 of 79.7 mg Bo/L for the fish P. promelas (Soucek et al, 2010) at pH range 7-5-8.5. This value is put forward for hazard assessment purposes. No data for other pH-ranges were identified.

For invertebrates, the following lowest reliable data point for boron (test organism: C. dubia) was a value of 119 mg B/L for pH-range 6.5-7.5 (Soucek et al, 2010), and a geometric mean (n=6) of 119 mg B/L for pH-range 7.5-8.5 (Soucek et al, 2010). No data for the pH-range 5.5-6.5.

For algae (P.subcapitata) there was one reliable acute data point, namely an 72h-EC50 of 52.4 mg B/L for the pH-range 7.5-8.5 (Hanstveit and Oldersma, 2000). No data for other pH-ranges were identified.

 

Summary of chronic freshwater data:

Relevant and reliable chronic no-effects values were identified for seventeen freshwater species: Micropterus salmoides, Oncorhynchus mykiss, Brachydanio rerio, Daphnia magna, Spirodella polyrhiza, Hyalella azteca, Xenopus laevis, Pimephales promelas, Ictalurus punctatus, Carassius auratus, Chironomus riparius, Brachionus calyciflorus, Rana pipiens, Selenastrum capricornutum, Anaxyrus fowleri, Ambystoma maculatum and Lampsilis silliquoidea.

No-effect levels for dissolved boron were situated between 6.3 mg Mo/L and 69.9 mg B/L, i.e., a difference of a factor of 11 between the most and least sensitive species. The zebrafish D.rerio and the amphipod H.azteca were the most sensitive trophic levels. The least sensitive species was the toad A.fowleri. A Species Sensitivity Distribution (SSD) has been developed for the assessment of boron the freshwater compartment, using the reliable species-specific chronic toxicity effect levels that have been generated in various research studies. 

Summary of chronic marine data:

Relevant and reliable chronic no-effects valus were identified for twenty-five freshwater data: Limanda limanda, Menidia beryllina, Cyprinodon vareigatus, Americamysis bahia, Litopenaeus vannamei, Anthocidaris crassipina, and 19 algal species (not further specified here). However, most of these toxicity data are based on nominal values and cannot therefore be considered for PNEC derivation. Marine waters contain about 5 mg B/L, so it may be expected that marine organisms are more tolerant of boron than freshwater organisms. However, the lack of a suitable database prevents direct evaluation of this expectation.

Additional information

  

Overview of most sensitive species-specific K1-NOEC/EC10-values for boron in the freshwater environment

Species Name	Species Name	Taxa	Added geomean NOEC/EC10(mg B/L)
Micropterus salmoides	Pisces – Chordata	Mortality	36.8
Oncorhynchus mykiss	Pisces – Chordata	Mortality	19.2
Brachydanio rerio	Pisces – Chordata	Growth	6.3
Daphnia magna	Crustacea	Reproduction	13.9
Spirodella polyrhiza	Higher plants	Growth rate	6.5
Hyalella azteca	Crustacea	Reproduction	6.3
Xenopus laevis	Amphibian – Chordata	Mortality, growth, reproduction	9.4
Pimephales promelas	Pisces – Chordata	Mortality	21.3
Ictalurus punctatus	Pisces – Chordata	Mortality	13.5
Carassius auratus	Pisces – Chordata	Mortality	30.3
Chironomus riparius	Insecta	Emergence	20.1
Brachionus calyciflorus	Rotifera	Reproduction	24.6
Rana pipiens	Amphibian – Chordata	Mortality	45.1
Selenastrum capricornutum	Chlorophyta	Growth rate	17.5
Anaxyrusfowleri (former name: Bufo fowleri)	Amphibian – Chordata	Mortality	69.9
Ambystoma maculatum	Amphibian – Chordata	Malformation	24.5
Lampsilis silliquoidea	Molluscs	Biomass	30.0

 

These data have been used for the construction of a Species Sensitivity Distribution (SSD) from which the median 5th percentile, i.e. the HC5,50% with 5%-95%-confidence interval was derived. The confidence interval is calculated using a Monte Carlo analysis on the log-normal distribution that was fitted through the 17 data points. The calculated HC5,50%-value is used for the freshwater PNEC-derivation (i.e., PNECaquatic= HC5,50%/ Assessment Factor). The value of this assessment factor depends on the uncertainty analysis that was conducted on this data set.

 

An in-depth discussion of the uncertainty analysis is given in the Background document “Environmental effects assessment of boron”, which is attached in the technical dossier in IUCLID Section 13. Based on this analysis - and taking sufficient conservatism into account - an Assessment Factor of 2 on the HC5,50% is put forward for the derivation of an aquatic PNEC.