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Books > Professional & Technical > Environmental engineering & technology > Sanitary & municipal engineering > Water supply & treatment
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Silver Biotic Ligand Model (BLM) - Refinement of an Acute BLM for Silver, Phase 2 (Paperback)
Loot Price: R3,218
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Silver Biotic Ligand Model (BLM) - Refinement of an Acute BLM for Silver, Phase 2 (Paperback)
Series: WERF Research Report Series
Expected to ship within 12 - 17 working days
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The biotic ligand model (BLM) is a computational tool that may be
used to predict toxic effect levels of metals, including Ag. The
BLM considers the effect of site-specific water quality
characteristics on Ag speciation and bioavailability. This provides
a basis for extrapolating from laboratory waters, used for most Ag
toxicity tests, to natural waters, where the bioavailability and
toxicity of Ag may differ. The original version of the BLM for the
acute toxicity of Ag was reviewed by the USEPA Science Advisory
Board (SAB) in 1999 and they recommended the completion of
additional Ag chemistry and toxicity studies to provide data to
test and refine the model. This project was completed to satisfy
these recommendations. A chemistry component was completed to
improve the representation of Ag speciation in natural waters and
to characterize the important effect of sulfide on Ag
bioavailability. These investigations added to the information that
was available to characterize Ag chemistry and provided a basis for
updating the earlier version of the Ag BLM. The BLM was also
calibrated to laboratory toxicity data that were generated for a
Ag-sensitive invertebrate, Ceriodaphnia dubia, a cladoceran that
had previously been tested to only a limited degree. The studies
were carried out in laboratory waters in which the chemistry was
systematically varied to provide a basis for calibration of the BLM
to the toxicity data for C. dubia. Toxicity tests were also
performed with both Pimephales promelas and C. dubia in natural
water samples that were well characterized chemically, with the
data then used to test the model. While the C. dubia BLM results
were relatively successful at simulating the observed effect levels
the P. promelas results highlighted the need for further testing
and refinement of the Ag BLM as it was applied to this fish
species. Physiological tests were performed to explore the apparent
increase in sensitivity of P. promelas in some of the test waters
that were relatively low in ionic strength. It was determined that
acclimation to such low ionic strength waters, in the absence of
Ag, did not significantly reduce their sensitivity to Ag. Rather,
it appeared that any benefit that may have been realized by
acclimation, such as an enhanced ability to upregulate ion uptake
rates in low ionic strength waters, was apparently offset by a
concomitant increase in the rate at which Ag was accumulated. The
Ag BLM was modified to account for the effect of low ionic strength
water on the sensitivity to Ag of > 4-day old P. promelas. This
led to an improved ability of the BLM to predict P. promelas effect
levels in the natural waters. Physiological tests were also
performed to investigate the apparent species-specific protection
against Ag toxicity that is provided by chloride. Investigations
with P. promelas suggested that the differences in degree of
protection may be related to differences in how Ag affects the
ionoregulation of Na+ and Cl- by different fish species. Although
questions remain with regard to chloride, it appears that the BLM
is able to predict this response reasonably well, particularly for
the relatively sensitive <4 day old P. promelas. In summary, the
WERF program yielded an improved chemistry and toxicity database,
including data over an extended range of water quality
characteristics and for an additional Ag-sensitive invertebrate,
thereby providing a basis for refining the acute Ag BLM and
improving its overall predictive ability.
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