Barium sulfate

Endpoint summary

Additional information

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

A PNECsoil is calculated on the basis of the lowest determined effect concentration. For barium, the lowest (long-term) NOEC was 211 mg/kg soil dw, and this for the collembole Folsomia candida (Kuperman et al, 2008). Other NOEC-values were 258 and 433 mg/kg soil dw, but these data were obtained for the same throphic level (soil invertebrates). No reliable NOEC-values for plants or soil micro-organisms were identified for Ba.

As a result, and assessment factor 100 needs to be applied on the lowest NOEC for PNEC-derivation (long-term data point for one trophic level). Therefore, bases on the assessment factor method, 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. Such data were also generated and reported in the FOREGS data set. The FOREGS monitoring survey represents more than 837 sampling locations covering the major part 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 analyzing all samples in the same laboratories.

A total number of 837 soil samples were analyzed, and the barium content in the soil samples ranged from 10 to 1669 mg Ba/kg dry wt. Country-specific median values were situated between 17.3 mg Ba/kg dry wt and 117.9 mg Ba/kg dry wt. The 90th percentiles for the different countries (i.e., the reasonable worst case (RWC) baseline levels) ranged between 33.5 mg Ba/kg dry wt and 331.5 mg Ba/kg dry wt.

As mentioned before, the RWC-ambient PEC of a site or region is compared with the PNEC for this element for regional risk characterisation purposes. Potential regional risks are identified when the RWC-ambient PEC exceeds the PNEC-value.

The RWC-ambient PEC represents the background/baseline levels 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 observed risks are caused by the addition of the anthropogenic fraction: it would be illogical that the ecosystem of a specific environmental compartment would be affected by the natural baseline concentration levels of a specific element/substance that are present in the environment.

In the specific case of Ba, however, the lowest country-specific RWC-baseline level already exceeds the PNECsoil of 2.11 mg/kg dry wt by almost one order of magnitude. This would mean that the whole European terrestrial compartment (and its ecosystems) may adversely be affected by natural baseline levels of barium. As such a finding makes no sense, it must be concluded that the proposed PNEC value of 2.11 mg Ba/kg dry wt for the terrestrial compartment is overly conservative. The main explanation is that the assessment factor of 100 on the derived NOEC of 211 mg/kg dry is excessively conservative, and leads to a PNEC that is not realistic.

The 25th and 75th percentiles of barium levels in the FOREGS data set for top soil samples are 40 mg/kg dry wt and 102 mg/kg dry wt, respectively, resulting in an outlier cut-off value of 415.3 mg Ba/kg dry wt. The outlier cut-off level is more than two orders of magnitude higher than the provisionally derived PNECsoil of 2.11 mg/kg dry wt. For the aquatic compartment, the provisional PNECaquatic was derived by dividing the outlier cut-off level by a factor of 2. Following a similar approach, the PNECsoil becomes 207.7 mg Ba/kg dry wt, and this value of 207.7 mg Ba/kg dry wt is considered as a reliable, provisional PNEC for the terrestrial compartment:

- The value of 207.7 mg Ba/kg dry wt is a factor of 1.4 higher than the overall 90th percentile of barium baseline levels in the terrestrial compartment. Therefore, no regional risk due to baseline barium levels is observed in Europe when the pooled dataset is evaluated.

- With exception of three countries (Czech Republic, Germany, Italy), the value of 207.7 mg Ba/kg dry wt is higher than the country-specific RWC-baseline PECs. Therefore, no regional risks due to RWC-baseline barium levels are observed in the majority of European countries when a country-specific approach is followed.

- The value of 207.7 mg Ba/kg dry wt is below the lowest NOEC that was determined by Kuperman et al (2008) for soil invertebrates, i.e., 211 mg/kg dry wt, and is therefore sufficiently protective for the evaluated test organisms (E. crypticus, E. fetida, F. candida).