Chronic BLMs for Ni have been developed in laboratory experiments for three different trophic levels (for the invertebrates Ceriodaphnia dubia and Daphnia magna, the fish Oncorhynchus mykiss, and the green alga Pseudokirchneriella subcapitata) (Deleebeeck et al., 2007; Deleebeeck et al., 2008; Deleebeeck et al., 2009). An additional BLM has been developed for the terrestrial higher plant Hordeum vulgare using hydroponic exposures (Lock et al., 2007).
The chronic BLMs were further validated in natural waters within specific boundaries selected to reflect the typical range (defined as the 10th to 90th percentile) of physico-chemical factors (pH, hardness, DOC) occurring in EU surface waters. It must be emphasized that the H. vulgare BLM has not been validated in natural waters, and therefore, this model should be used with caution.
The results of the BLM development/validation experiments indicated that both Ca2+ and Mg2+ (which together comprise the water quality characteristic known as “hardness”), H+ (expressed as pH), and DOC affected Ni toxicity. The same trends were observed for all of the species tested:
- as pH ↑, toxicity ↑
- as hardness ↑, toxicity ↓
- as DOC ↑, toxicity ↓
The consistency in trends has not been observed for all metals (e.g., Cu) and offers empirical evidence that the mechanisms of Ni toxicity are conserved across algae, invertebrates, and fish.