Barium chloride

Toxicity to birds

Description of key information

Based on the findings by Schwarzbach et al (2006) and Ridgeway and Karnofsky (1952), elevated barium concentrations in eggs may result in deformations of the feet and malpositioning of the embryo in the egg

Additional information

Schwarzbach et al (2006) reported Ba-levels in eggs of the California Clapper Rail (Rallus longirostris obsoletus) collected at the San Francisco Bay (South Bay and North Bay) (period: 1992 at S-B and 1998 at N-B):

- Ba-levels in eggs collected at the South Bay were situated between <0.1 and 0.59 μg/g dw, with a mean value of 0.34 μg/g; Ba-levels exceeded the detection limit of 0.1 μg/l in 36 of the 38 analysed eggs.

- Ba-levels in eggs collected at the North Bay were situated between <0.2 and 4.1 μg/g dw. Ba-levels exceeded the detection limit of 0.2 μg/l in 8 of the 9 analysed eggs. Here, three embryos with deformities of the feet were found, and these effects were associated with the highest Ba-levels, ranging from 2.2 to 4.1 μg/g.

Mean Ba-concentration in normal, late-stage embryos (n=12) was 0.41 μg/g (range: 0.20–0.59 μg/g), whereas the mean Ba-concentration in deformed, late-stage embryos (n=3) was 3.00 μg/g (range: 2.16–4.13 μg/g). This difference proved to be significant, but it should be noted that similar, significant findings were also observed for other trace elements that were determined, i.e., aluminium, strontium and chromium. The non-deformed late-stage embryos had Ba-concentrations that were similar to the concentration range reported for Light-footed Clapper rails in southern California by Hui et al (2002). Higher Ba-levels in eggs were also – though not significant – associated with malpositioning of late-stage embryos. Mean Ba-levels of 1.28 and 0.51 μg/g were found in malpositioned and normal late-stage embryos, respectively. The egg with the maximum Ba-concentration of 4.1 μg/g was both deformed and malpositioned. Schwarzbach et al (2006) pointed out that the concentration of Ba (and other trace elements that interact with Ca or phosphate metabolism) was somewhat dependent on the stage of embryo development, with the latter stages having higher concentrations of these elements. Mobilization of Ba from the shell during embryo development seems likely, because the embryo extracts minerals from the shell for the developing skeleton (Tuan, 1987).

This specific terata for barium, i.e., malformation of the feet, was also noted by Ridgway and Karnofsky ((1952) who directly injected barium (as BaCl2) into the yolk of 4d or 8d old eggs, or onto chorioallantoic membrane (CAM). This malformation of the toes occurred irregularly, but was seen in about 50% of the treated embryos (8d old injection of yolk or CAM administration) that survived to 18 days. None of the embryos injected at 4 days showed toe abnormalities, and no other gross effects were noted on the embryo. It should be noted that this type of administration (i.e., direct injection into the yolk or onto the CAM) are no relevant uptake routes. The LD₅₀ for 4d-old eggs ‘injection in the yolk) was >20 mg/egg. For the 8d-old egg and administration via the CAM, the LD₅₀ was approximately 11 and 0.8 mg/egg, respectively.

Malformation of the feet has not been observed for other elements that were significantly elevated in deformed embryos. This strongly suggests that Ba was responsible for some of the observed malformations in the eggs collected at North Bay (Schwarzbach et al, 2006).

Custer et al (2001) reported trace element concentrations in eggs that were collected at two locations along the North Platte River. Mean barium levels in eggs from the tree swallow (n=7) and the house wren (n=6) were 4 and 7 μg/g dry wt, respectively. Barium levels in wren were significantly higher than in swallow eggs (p=0.04; two-way ANOVA overall p<0.05). Ba-levels in eggs were also higher at the reference site (7.7 μg/g dry wt) than at the refinery site (3.8 μg/g dry wt), but may be related to the Ba-content in different environmental compartments: Ba-levels in the sediment at the reference site and refinery site were 211 and 173 μg/g dry wt, respectively. Although these levels are higher than those that reportedly caused terata to the feet, no observations of such deformities were mentioned by Custer et al (2001). A possible explanation could be that no late-stage embryos were considered in this study, or that the investigate species are less susceptible to elevated Ba-levels.

Mora (2003) collected eggs (n=70) of passerine birds at four locations in Arizona (USA). Levels of Ba and nine other inorganic elements in eggs and eggshells were reported. Barium was on average 10-20 times more concentrated in the eggshell than in egg contents. Mean Ba-levels in the eggs (data grouped per species and per location) ranged from 0.4 to 14.3 μg/g dry wt. Ba-levels in eggshell were situated between 2.9 and 73.8 μg/g dw. Ba-levels in the sediments of these locations were 87, 101, and 204 mg/kg dry wt.

It is noteworthy that large differences can be noted for different species:

- At Roosevelt, the mean barium content in eggs of the yellow warbler (n=4) was 14.3 μg/g, but the mean for the Bell’s vireo (n=6) was 3.2 μg/g.

- Grouping all data for the yellow-breasted chat (n=21), the mean Ba-content in egg and eggshell were 2.5±2 μg/g and 33.9±23 μg/g, resulting in an eggshell/egg ratio of 13.6. For the willow flycatcher (n=5), a similar analysis resulted in a mean Ba-content of 0.5±0.1 μg/g and 3.6±2.2 μg/g for egg and eggshell, respectively, and an eggshell/egg ratio of 7.2.

Additional data on Ba-levels in eggshells of nine passerine birds from different regions in Arizona were reported in Mora et al (2007), but no relationship between these levels and potential adverse effects (deformities, eggshell thickness) were demonstrated. Species-mean Ba contents in the eggshells ranged from 26 μg/g dry wt (lesser goldfinch,Carduelis psaltria) to 88±42 μg/g dry wt (brown-headed cowbird,Molothrus ater)