Development of a Biotic Ligand Model and a Regression Model Predicting Acute Copper Toxicity to the Earthworm Aporrectodea caliginosa

Abstract

The purpose of this study was to develop a terrestrial biotic ligand model (BLM) for predicting acute copper toxicity to the earthworm Aporrectodea caliginosa. To overcome the basic problems hampering development of BLMs for terrestrial organisms, an artificial flow-through exposure system was developed consisting of an inert quartz sand matrix and a nutrient solution, of which the composition was univariately modified. A. caliginosa was exposed for 7 days under varying concentrations of copper and the major cations modifying toxicity: H+, Ca2+, Mg2+, and Na+. In addition copper speciation was modulated by means of EDTA or dissolved organic carbon (DOC). An increase in pH or pNa resulted in a linear decrease of 7-days median lethal concentrations. Increasing Ca2+ and Mg2+ activities had inconsistent effects. EDTA addition decreased toxicity when the total copper concentration in the pore water was kept the same. This is attributed to the strong complexation capacity of EDTA and shows that total copper is not the toxic species. DOC was more protective than could be explained by its metal complexing properties. The BLM developed incorporates the effects of H+ and Na+. This BLM was validated with the results of a set of bioassays with artificial pore water in quartz sand and by a set of bioassays in spiked field soils. Prediction error was within a factor of 2, but some predictions were not within the 95% confidence interval. Therefore a more widely applicable regression type model was developed that was able to explain >95% of the (lack of) toxicity observed. To our knowledge this is the first report of the successful development of a terrestrial BLM.

Modelling the effects of copper on soil organisms and processes using the free ion approach: Towards a multi-species toxicity model

“…Protective effects 415 of Mg 2+ and Ca 2+ against Cu toxicity have been previously observed, for example by 416 Kinraide et al (2004) and Luo et al (2008) for root elongation of wheat (Triticum 417 aestivum) in nutrient solutions. On the other hand, Steenbergen et al (2005) found 418 that Mg 2+ and Ca 2+ did not protect the earthworm A. caliginosa against the acute 419 toxicity of Cu 2+ but appeared to contribute to the toxicity. They suggested that co-420 variance between H + , Mg 2+ and Ca 2+ activities was at least partly responsible for these 421 observations.…”

“…The BLM was originally 64 developed to describe the acute toxic effects of metal accumulation at the gill of fish, 65 but has been applied to toxicity data for a number of other aquatic organisms. Some 66 progress has been made in applying the principles of the BLM to soil-dwelling 67 organisms: acute BLMs have been developed for soil organisms such as the 68 earthworm Aporrectodea caliginosa (Steenbergen et al, 2005) …”

Quantitative arsenic speciation in two species of earthworms from a former mine site

“…Earthworms are of particular use in monitoring the potential exposure of single or multiple soil 30 contaminants as they maintain constant contact with both the solid and liquid phase of soil. In this way, earthworms can be used in partitioning and chemical speciation models to assess bioavailability [2][3][4][5] and the basis for toxic effects 6,7 .…”

Toxicodynamics of copper and cadmium inFolsomia candidaexposed to simulated soil solutions

“…For plants, toxicity to particularly wheat (Triticum aestivum), pea (Pisum sativum), and barley (Hordeum vulgare) has been reported using different test solutions and different metal salts [4,[9][10][11]. The use of aqueous solutions has also been reported for different earthworm species [3,12,13]. Few studies have been performed on other soil organisms (M.M.…”