Barium chloride

Endpoint summary

Additional information

The same assessment factors used for the aquatic compartment are applied to the terrestrial compartment. The applied assessment factor depends on the available data, i.e., short-term or long-term toxicity data, number of trophic levels tested and general uncertainties in predicting ecosystem effects from laboratory data. A dataset comprising of toxicity data for primary producers, consumers and decomposers is preferred. 

 

Reliable barium toxicity data are reported in the table below.

Table1. Overview of reliable chronic soil toxicity data for barium

Species	Parameter	Endpoint	Value (mg Ba/kg dw)	Reference
Eisenia fetida (annelid)	reproduction	21-d NOEC	258 (meas.)	Kuperman et al. (2006)
Enchytraeus crypticus(annelid)	reproduction	21-d NOEC	433 (meas.)	Kuperman et al. (2006)
Folsomia candida(springtail)	mortality, reproduction	28-d NOEC	211 (meas.)	Kuperman et al. (2006)

Long-term toxicity data are available for one trophic level only, i.e. soil invertebrates (arthropods and annelids). The PNECsoil is derived using the lowest available effect concentration, i.e. the 28-d NOEC of 211 mg Ba/kg soil dw for reproduction and mortality of the springtailFolsomia candida(Kuperman et al, 2006) in a sandy loam soil. The soil was selected because it has physico-chemical characteristics that support relatively high bioavailability of cationic metal, including low organic matter and clay contents. Thus, an assessment based on this NOEC value is conservative. Other NOEC-values for the same trophic level (soil invertebrates) amount to 258 and 433 mg/kg soil dw for reproduction ofEisenia fetidaandEnchytraeus crypticus(both annelids) in the same soil as tested with springtails. Reliable NOEC or EC10-values for the toxicity of barium to plants or soil micro-organisms were not identified.

In accordance with ECHA guidance (Chapter R.10, 2008), an assessment factor of 100 needs to be applied if long-term toxicity data are available for one trophic level only. Thus, a PNECsoil of 2.11 mg Ba/kg soil dw is determined.

The relevance of this value can be assessed by comparing the estimated PNECsoil with baseline levels of barium in pristine European topsoil samples as reported in the FOREGS data set. The FOREGS monitoring survey represents more than 837 sampling locations covering major parts of Europe. Detailed descriptions of sampling methodology, sampling preparation and analysis are given in Salminen et al. (2005). High quality and consistency of the obtained data were ensured by using standardized sampling methods and by treating and analysing all samples in the same laboratories.

A total number of 837 soil samples were analysed, and the barium content in the soil samples ranged from 10 to 1669 mg Ba/kg dw. Country-specific median values ranged from 17.3 to 117.9 mg Ba/kg dw. The 90^thpercentiles of different countries (i.e., the reasonable worst case (RWC) baseline levels) ranged from 33.5 to 331.5 mg Ba/kg dw.

The RWC-ambient PEC of a site or region is compared to the PNEC in order to assess regional risks. A potential regional risk is identified when the RWC-ambient PEC exceeds the PNEC-value.

The RWC-ambient PEC represents the background/baseline level of an element/substance to which the anthropogenic fraction (local point sources and diffuse sources) of this element/substance is added. It is expected that potential risks are solely due to anthropogenic additions of this element/substance. It can further be assumed that in an ecosystem, natural baseline levels of a specific element/substance would not exert toxic effects in a specific environmental compartment of that ecosystem.

The lowest country-specific RWC-baseline level of 17.3 mg Ba/kg dw exceeds the PNECsoil of 2.11 mg/kg dw by almost an order of magnitude. This would mean that either the proposed PNECsoil of 2.11 mg Ba/kg dw is unrealistically low or all European soils are impaired by natural baseline barium level. Thus, it may be assumed that the application of an assessment factor of 100 to the lowest NOEC of 211 mg/kg dw is excessively conservative and results in an unrealistic PNEC.

Setting a more realistic PNEC requires a better understanding of what concentration background/baseline levels can be considered “normal” in soils. Data from the FOREGS data are analysed to set an outlier cut-off level: values below this cut-off level are considered “normal and representative”, whereas values exceeding this cut-off level are considered as outliers that do not represent normal environmental properties. Such an outlier cut-of level may serve as a starting point for setting a more realistic PNEC that still remains sufficiently conservative.

According to the ECHA REACH Guidance document on information requirements and chemical safety assessment –Chapter R.16: Environmental Exposure Estimation (ECHA, 2008), the outlier cut-off level can be determined with the following formula:

log(Xi) > log (p75) + K(log(p75) – log(p25))

with Xi being the concentration above which a measured concentration may be considered an outlier, pi the value of the ith percentile of the (non-parametric) distribution and K a scaling factor. A scaling factor K=1.5 is applied, as this value is used in most statistical packages.

The 25^thand 75^thpercentile of barium levels in top soil samples from the FOREGS data set are at 40 and 102 mg/kg soil dw, respectively, and the outlier cut-off value amounts to 415.3 mg Ba/kg dw. The outlier cut-off level is more than two orders of magnitude higher than the provisionally derived PNECsoil of 2.11 mg/kg dw.Afactor of two is applied to the cut-off level and a PNECsoil of 207.7 mg Ba/kg dw is derived andconsidered to be a provisional yet reliable PNEC for soil.

- The PNEC value of 207.7 mg Ba/kg dw is by a factor of 1.4 higher than the overall 90^thpercentile of barium baseline soil levels. Thus, a regional risk based on baseline barium levels can be excluded in Europe when the pooled dataset is evaluated.

- With exception of three countries (Czech Republic, Germany, Italy), the PNECvalue of 207.7 mg Ba/kg dw is higher than the country-specific RWC-baseline PECs. Therefore, a regional risk based on RWC-baseline barium levels is not estimated in the majority of European countries when a country-specific approach is followed.

- The PNEC value of 207.7 mg Ba/kg dw is below the lowest NOEC of 211 mg/kg dw that was determined by Kuperman et al (2006) for soil invertebrates (E. crypticus, E. fetida and F. candida). Thus, thePNEC value of 207.7 mg Ba/kg dw is sufficiently protective for the evaluated soil invertebrates in a sandy loam soil with a relatively high bioavailability.