Disodium octaborate

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Qualifier:

no guideline followed

Principles of method if other than guideline:

50 species (58 varieties) were grown in each of 6 large outdoor sand cultures supplied respectively with a trace (0.03-0.04 ppm), 1, 5, 10, 15, 25 ppm of boron.

GLP compliance:

not specified

Radiolabelling:

no

Vehicle:

no

Test organisms (species):

other: 50 different species reported

Details on test organisms:

TEST ORGANISM
- 50 different species
- Seeds planted directly in the sand and supplied from the start with culture solutions containing different boron concentrations

Details on test conditions:

TEST SYSTEM
- Test container (material, size): 6 large sand cultures

Type:

BCF

Value:

12 - 155 L/kg

Details on results:

- Behavioural abnormalities: Plants died, leafs were burned depending on the concentration and the species
- Observations on body length and weight: Depending on the concentration some plants showed deficiency and others toxicity

Reference 2

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2000-2003

Reliability:

2 (reliable with restrictions)

Principles of method if other than guideline:

Several cultivars of poplar and willow were planted in site (New Zealand) contaminated with wood waste and monitored over three years. Boron concentrations in leaves and stems were monitored, as well as in the substrate.

GLP compliance:

no

Details on sampling:

Poplar tree heights measured annually to determine 25th, 50th and 75th percentile for tree height, then 3 specimens of each of 3 clones were destructively sampled for dry biomass and boron content of stems and leaves. Substrate sampled from root zone of each tree at depth of approx 5 cm.

Test organisms (species):

other: Clones of poplar and willow hybrids, and Eucalyptus

Details on test organisms:

Populus deltoides x nigra "Argyle" & "Selwin"; P. deltoides x yunnanensis "Kawa"; Populus euramericana x yunnanensis "Toa"; Populus alba x glandulos "Yeogi"; P. nigra x mamimowic "Shinsei"; Salix matsudana x alba "Tangoio"; Salix kinuyangi; Salix purpurea; Eucalyptus fastigata; E. nitens

Details on results:

Average for all (3) trees (n=21): wood waste - 30 mg-B/kg, stem - 21 mg B/kg, and leaf - 845 mg B/kg. The authors did not calculate bioaccumulation factors, but using these values, the BAF for stem would be 0.7 and the BAF for leaves would be 28.2

Values for different varieties: (Table 3 of publication)

Kawa (n=7): substrate (wood waste) - 31 mg-B/kg, stem - 29 mg B/kg, and leaf - 827 mg B/kg.

Toa (n=6): substrate (wood waste) - 36 mg-B/kg, stem - 22 mg B/kg, and leaf - 1012 mg B/kg

Yeogi (n=8): substrate (wood waste) - 28 mg-B/kg, stem - 20 mg B/kg, and leaf - 776 mg B/kg.

Reference 3

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Principles of method if other than guideline:

Adult male mallard ducks were exposed to dietary concentrations of 1,600 ppm boron as boric acid and estimated the tissue accumulation and loss rates when the ducks were returned to uncontaminated food.

GLP compliance:

not specified

Details on sampling:

- Sampling intervals/frequency for test organisms: One bird from each of the 15 pens was randomly selected and sacrificed 0, 1,2,4, 8, 16, 32, and 48 d after feeding with treated diets began. After 48 d on treated diets, all remaining birds were fed the control diet for the remainder of the study. Following a pattern similar to that used in the accumulation phase of the study, one bird from each pen was sacrificed 1,2,4, 8, 16, 32, and 48 d after the switch to control food.
- Sampling intervals/frequency for test medium samples: Small (20 g) composite samples of feed from all batches mixed on the same day were saved for chemical analysis of boron.

Details on preparation and application of test substrate:

Boric acid powder was mixed directly with the feed

Test organisms (species):

other: Anas platyrhynchos

Details on test organisms:

TEST ORGANISM
- Common name: Mallard ducks
- Source: A commercial game farm
- Age at test initiation (mean and range, SD): adult

ACCLIMATION
- Acclimation period: 2 weeks

Total exposure / uptake duration:

48 d

Total depuration duration:

48 d

Details on test conditions:

TEST SYSTEM
- Test container (material, size): 2.5 x 6.5 m pens
- No. of organisms per container (treatment): 15
- No. of replicates per treatment group: 4
- No. of replicates percontrol / vehicle control: 3


RANGE-FINDING / PRELIMINARY STUDY
- Test concentrations: 1600 ppm boron
- Results used to determine the conditions for the definitive study: These dietary levels of boron were selected because mallards, both ducklings and adults, tolerate them without excessive mortality; also, they cause physiological and behavioral effects in mallards, and they approximate the maximum levels in aquatic plants consumed by waterfowl in areas exposed to agricultural drainwater in the Central Valley of California.

Nominal and measured concentrations:

Nominal concentration : 1600 ppm
Measured concentration : 1615 ppm average

Type:

BCF

Value:

0.02 dimensionless

Basis:

organ d.w.

Remarks on result:

other: liver

Type:

BCF

Value:

0.02 dimensionless

Basis:

organ d.w.

Remarks on result:

other: brain

Type:

BCF

Value:

0.04 dimensionless

Basis:

organ d.w.

Remarks on result:

other: blood

Reported statistics:

The ability to predict levels of arsenic and boron in the liver from levels in the blood was described with linear regression. The possibility that these relationships differed by treatment groups was tested with analysis of covariance (ANCOVA).

The authors reported BCF values < 0.1 and noted that liver and blood residues were eliminated within 1 day on a "clean diet".

Reference 4

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Qualifier:

no guideline followed

Principles of method if other than guideline:

One hundred and twenty-six pairs of breeding mallards were fed diets supplemented with boron at 0, 450, or 900 ppm in combination with Se at 0, 3.5, or 7 ppm, in a replicated factorial experiment. Ducklings produced received the same treatment combination as their parents.

GLP compliance:

not specified

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: the eighth egg was removed from each nest and 14d after hatching the ducklings and their parents were euthanized. Samples of liver, kidney, and spleen from 10 randomly selected hens, drakes, and ducklings were saved in 10% buffered formalin.
- Sample storage conditions before analysis: content of eggs were frozen, ducklings and parents were weighted and the liver removed, weighted and frozen for analysis
- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods):

Vehicle:

no

Test organisms (species):

other: Anas platyrhynchos

Details on test organisms:

TEST ORGANISM
- Common name: mallards
- Source: Outdoorsman Hunting Club, Webb, IA, USA
- Age at test initiation (mean and range, SD): 1-year-old
- Weight at test initiation (mean and range, SD):


ACCLIMATION
- Acclimation period: 17 days
- Feeding : untreated diet of commercially available developer mash
- Females were kept under controlled lighting (8h/d) to delay the onset of egg laying and to synchronize their cycles

Total exposure / uptake duration:

ca. 120 d

Details on test conditions:

TEST SYSTEM
- Test container (material, size): 1m² outdoor pens
- No. of organisms per container (treatment): 1
- No. of replicates per treatment group: 14
- No. of replicates percontrol / vehicle control: 14

Nominal and measured concentrations:

Added concentrations in diet are 450 and 900 ppm boron

Type:

BCF

Value:

0.03 dimensionless

Basis:

organ d.w.

Remarks on result:

other: adult liver

Type:

BCF

Value:

0.05 dimensionless

Basis:

organ d.w.

Remarks on result:

other: whole eggs

Details on results:

- Observations on body length and weight: weight loss in females between treatment onset and pairing (3 weeks) in the 900-ppm treatment group
- Other biological observations: egg weight and egg fertility were lower in the 900-ppm treatment group

Reported statistics:

Data were analyzed by logistic regression under a mixed effects model with parameters for main and interactive effects between Band Se, and a pen effect. Parameters were tested for significance with F tests; multiple comparisons were made using contrasts. All remaining response wariables were analyzed by analysis of variance under a model appropriate for the main effects and interactions being tested and an error term suitable for unbalanced data. Tests of hypotheses that included more than one bird per pen were made with F tests under a mixed effects model using an appropriate error term. All other F tests assumed a fixed effects model and used the residual mean square as the error term. Normality of residuals was evaluated using the Shapiro-Wilk statistic and normal probability plots. Studentized residuals were plotted to assess homoscedasticity. Data that did not meet normality or homosccedasticity assumptions necessary for ANOVA were transformed so as to meet the assumptions. Consequently, all percentage data were arcsine transformed and all residue data were log. transformed before analysis. Multiple comparisons were made using Tukey's multiple comparison procedure (MCP) at alpha = 0.05.

Boron accumulates rapidly in adult mallard liver and is estimated to take 2.8d to reach 95% of its asymptotic level. On a dry-weight basis, B in adult liver in the control, 450 -, and 900 -ppm B treatments groups was 2, 15, and 27 ppm, respectively.

Dry-weight concentrations of B in eggs were 0.6, 22, and 38 ppm in the B control, and 450- and 900 -ppm treatment groups, respectively.

Reference 5

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Qualifier:

no guideline followed

Principles of method if other than guideline:

Barley (Hordeum vulgare L.) was grown in pots of a sandy soil to which six levels of boron were added. Plant tissues collected from each harvest were analysed for boron concentrations

GLP compliance:

not specified

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: sampling at three times of plant harvest: early tillering, booting, and maturity stage

Vehicle:

no

Details on preparation and application of test substrate:

- Method of application to soil surface (if used): Basal nutrient dressings of 300 mg KH2PO4, 300 mg KNO3, 400 mg CaCl2, 60 mg MgSO4.7H2O, 17.5 mg ZnSO4.7H2O, 17.5 mg CuSO4.5H2O, 45 mg MnSO4.H2O, and 0.428 mg Na2MoO4.2H2O were applied in solutions to the surface of soil in each pot. Boron solutions were also applied to the surfaces.
- Method of mixing into soil (if used): After the soils had dried, the nutrients were thoroughly mixed through the soils by shaking in a plastic bag.

Test organisms (species):

other: Hordeum vulgare L.

Details on test organisms:

B concentration of germinating seeds : 3 µg/g

Total exposure / uptake duration:

35 - ca. 120 d

Test temperature:

The pots were maintained near 18°C by immersion in root cooling tanks until harvest 2. Thereafter, the pots were placed on benches in an air-conditioned glasshouse.

Details on test conditions:

TEST SYSTEM
- Test container (material, size): polythene bags in undrained plastic pots of 16.5 cm surface diameter
- Amount of soil or substrate: 3.5 kg
- No. of organisms per container (treatment): 20 germinating seeds thinned to ten plants on day 12
- No. of replicates per treatment group: 3

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographical reference of sampling site (latitude, longitude): virgin sandy soil from Lancelin
- Depth of sampling: 0-10 cm
- Soil texture
- % clay: 3.5
- pH: 1:5, soil:water, 5.6
- Organic carbon (%): 0.69

Nominal and measured concentrations:

Nominal : 0, 0.5, 1, 2, 4, 8 µg B/g
Measured : <0.5, <0.5, <0.5, 1.0, 2.1, 4.9 µg B/g (mannitol extracted concentrations)

Type:

BCF

Value:

123 other: g/g

Basis:

organ d.w.

Remarks on result:

other: leaves

Type:

BCF

Value:

44 other: g/g

Basis:

organ d.w.

Remarks on result:

other: whole shoots

Type:

BCF

Value:

70 other: g/g

Basis:

organ d.w.

Remarks on result:

other: straw

Type:

BCF

Value:

2.1 other: g/g

Basis:

organ d.w.

Remarks on result:

other: grain

Type:

BCF

Value:

49 other: g/g

Basis:

organ d.w.

Remarks on result:

other: shoots

Type:

BCF

Value:

5 other: g/g

Basis:

organ d.w.

Remarks on result:

other: roots

Concentrations of B (µg B/g) were measusred in leaves, whole shoots, straw, grain, shoots and roots. An overview of the added B concentrations in soils, the concentrations in plant material and the BCF values are summarized below. Riley et al did not calculate BCF values. Based on the data presented the BCF's can be calculated.

B conc. in soil (µg/g)	B conc. in leaves (µg/g)	BCF for leaves (g/g)	B conc. in whole shoots (µg/g)	BCF for whole shoots (g/g)	B conc. in straw (µg/g)	BCF for straw (g/g)
0.5	50	100	19	38	54	108
1	92	92	39	39	52	52
2	210	105	88	44	120	60
4	520	130	190	48	260	65
8	1500	188	390	49	510	64

B conc. in soil (µg/g)	B conc. in grain (µg/g)	BCF for grain (g/g)	B conc. in shoots (µg/g)	BCF for shoots (g/g)	B conc. in roots (µg/g)	BCF for roots (g/g)
0.5	2	4	19	38	5	10
1	3	3	38	38	7	7
2	3	2	89	45	7	4
4	4	1	230	58	8	2
8	6	1	540	68	18	2

Additional information

Boron is known to be a critical element for the normal growth and productivity of terrestrial plants. Boron is required in plants for normal metabolic functioning of sugar transport, cell wall synthesis, lignification, carbohydrate metabolism, RNA metabolism, respiration, indole acetic acid (growth regulator) metabolism, phenol metabolism, the integrity of membranes, and the pollination process (Marschner, 1995). There is a certain minimum requirement of boron for a plant. However, there are considerable interspecies differences in the levels required for optimal growth. Monocotyledons generally require less than dicotyledons (Gupta et al, 1985).

Boron uptake varies with stage of growth and the concentration varies among the plant parts (Gupta et al, 1985). Plants also are known to change soil pH locally by root exudates to enhance uptake of essential nutrients (Reimann et al. 2001, WHO 1998).

The uptake mechanism has long been debated. It was first suggested that boron moves to the root surface in the soil solution by mass flow and enters the roots by passive diffusion (Bingham et al, 1970). However this concept has been challenged by Bowen (1968, 1969, 1972), Bowen and Nissen (1977), and Reisenauer et al (1973). They indicated that boron is actively absorbed in ionic form particularly when the boron concentration in soil is low (Gupta et al, 1985). This has been confirmed by more recent studies, which provided evidence for channel- and/or transporter-mediated boron transport systems (Tukano et al, 2005). The isolation of the boron transporter in BOR1-1 mutant plants showed elevated sensitivity to boron deficiency, especially in young growing organs in shoots. BOR1 is a membrane protein that belongs to the bicarbonate transporter superfamily (Takano et al, 2002; Frommer et al 2002).

Takano et al (2005) found that the activity of the BOR1 plasma membrane transporter for boron in plant is regulated (endocytosis and degradation) by boron availability, to avoid accumulation of toxic levels of boron in shoots under high boron supply, while protecting the shoot from boron deficiency under boron limitation.

Once in the plant, boron is passively carried in the transpiration stream to the leaves where the water evaporates and boron accumulates. This explains why boron concentrations are generally lower in roots, stems, and fruits than in leaves (WHO 1998). Once assimilated by the plant, boron becomes one of the least mobile micronutrients (Wolg 1940, Eaton 1944, Dible and Berger, 1952). Since boron is not readily transported from old to young plant parts, the earliest deficiency symptoms are found in young parts while the earliest toxicity symptoms are found in the old plant parts (Gupta et al, 1985).

Please also refer to the read-across statement attached to section 13.