Effects of sediment geochemical properties on heavy metal bioavailability.

Diagnosis of soil contamination using microbiological indices: A review on heavy metal pollution.

R. LAL and M.J. SHUKLA. Marcel Dekker, Inc., New York. 2004. Hardbound, 716 pp. $94.95. ISBN 0-8247-5324-0.

In the preface to their book, Principles of Soil Physics , authors Lal and Shukla state that the text is intended to focus on “soil's physical, mechanical, and hydrological properties, such

Principles of Soil Physics.

Diversity and abundance of ammonia-oxidizing archaea and bacteria in polluted mangrove sediment.

Biotic ligand model development predicting Zn toxicity to the alga Pseudokirchneriella subcapitata: possibilities and limitations

Inhibitory experiments were conducted to investigate the responses of the population sizes of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and the potential nitrification rates (PNRs) to Cu contamination in four Chinese soils. PNR was determined using a substrate-induced nitrification (SIN) assay, and the population size of the nitrifiers represented by amoA gene abundances was quantified using a real-time polymerase chain reaction (qPCR) assay. Both population size and PNR of the ammonia oxidizers reduced considerably at high Cu concentrations in all the soils. Bacterial amoA gene abundance was reduced by from 107-fold (Hailun soil) to more than 232-fold (Hangzhou soil) at the highest Cu concentrations (2,400 mg kg−1 Cu for Hailun, Langfang and Guangzhou soils and 1,600 mg kg−1 Cu for Hangzhou soil), while reduction in archaeal amoA gene abundance was from 10-fold (Langfang soil) to 89-fold (Hangzhou soil). AOA seemed more tolerant to Cu contamination than AOB. Nitrification rates were inhibited by more than 50% at a Cu concentration of 600 mg kg−1, and by more than 90% at the highest Cu concentrations in all soils. These results indicated that both AOA and AOB can be inhibited by toxic metals, highlighting the need to consider the role of AOA in nitrification in soils.

Do ammonia-oxidizing archaea respond to soil Cu contamination similarly asammonia-oxidizing bacteria?

Copper toxicity in 17 Chinese soils was screened using a substrate-induced nitrification assay to generate information for the development of a terrestrial biotic ligand model (tBLM). The leaching effect on the Cu toxicity thresholds was investigated. Both the total Cu-based median effective concentration (EC50) values (46.9–2726 mg/kg) and the solution Cu-based EC50 values (0.04–2.91 mg/L) in unleached soils varied substantially among the soils in the present study. For unleached soils, linear stepwise multiple regression analysis showed that total Ca and soil pH were the best predictors for total Cu-based EC50, while electrical conductivity (EC) and soil pH were the best predictors for solution Cu-based EC50. The variation in solution Cu-based EC50 was largely (R2 = 0.75) explained by Mg but not Ca and H+ concentration in soil solution at EC50, suggesting a protective effect of Mg2+ against Cu toxicity in the test soils. Leaching impacted Cu toxicity differently among the soils and apparently reduced the variations of both the total Cu-based and the solution Cu-based EC50. The predictability of the Cu EC50 by empirical models was decreased after leaching. The leaching effect on Cu toxicity, indicated by a leaching factor, was not predicted by any soil properties. There is a need to investigate quantitatively the mechanisms for the leaching effect on Cu toxicity in soils. Environ. Toxicol. Chem. 2010;29:294–300. © 2009 SETAC

https://setac.onlinelibrary.wiley.com/doi/pdf/10.1002/etc.51

Copper toxicity thresholds in Chinese soils based on substrate-induced nitrification assay

Deriving toxicity thresholds through bioassays has become the scientific basis for the risk assessment of metal contamination in soils, but few studies have been reported for Ni toxicity in Chinese soils. In addition, although leaching has been recommended to increase the ecological relevance of the output of soil toxicity bioassays, its impacts on Ni threshold and soil solutions in soils remained to be shown. Therefore, in this study, 17 soils were collected throughout China and were assessed for Ni toxicity using substrate-induced nitrification (SIN) assay for both un-leached and leached treatments. Meanwhile, soil solutions of all Ni treatments were extracted and analyzed. This study provides information for the development of a terrestrial biotic ligand model (TBLM) for Ni in Chinese soils. Soils were artificially amended with NiCl2 solution to generate nominal Ni contamination levels, and aliquot of each Ni treatment was leached with artificial rain to prepare leached soil samples. All the 17 un-leached and the 17 leached soils were subjected to the standard SIN protocol. A total of 816 microcosm tubes were established. Soil solution was extracted, and the solution physiochemical properties were analyzed for each Ni treatments. Both the total-Ni-based and the solution-Ni-based median effective concentrations (EC50) in un-leached soils and leached soils were calculated from dose–response curves. Free-Ni2+-based EC50 was also calculated based on solution chemical properties. Leaching effect was assessed based on these results. Ni EC50 varied largely among soils for both the total-Ni-based and the solution-Ni-based EC50 in un-leached soils. In un-leached soils, the total-Ni-based EC50 values ranged from 52.8 mg kg−1 (Hulunber soil) to 2,385.4 mg kg−1 (Wulumuqi soil), and the solution-Ni-based EC50 ranged from 0.70 mg L−1 (Jiaxing soil) to 293.35 mg L−1 (Wulumuqi soil). Stepwise multiple regressions showed that soil pH and total Ca were the best predictors for the total-Ni-based EC50. Protective effects of Ca2+ and Mg2+ but not H+ against Ni toxicity in soil solution were found. Leaching impacted Ni EC50 differently among soils, with leaching factor ranging from 0.2 (Haikou soil) to 19.7 (Hulunber soil) for the total-Ni-based EC50 and from 0.1 (Dezhou soil) to 35.7 (Jiaxing soil) for the solution-Ni-based EC50. In addition, predictability of Ni EC50 was higher in leached soils. The variations in Ni EC50 were in agreement with the findings in previous studies. Soil pH and Ca may play important roles in the partition of Ni in Chinese soils and thus impact the Ni toxicity. Protective effects of Ca2+ and Mg2+ in soil solutions against Ni toxicity may exist, but the role of H+ remained to be justified. The inconsistent impact of leaching on the free Ni2+ concentration at low Ni doses and the two competing effects of loss of salts in soil solution on Ni EC50 can partly account for the variation in leaching factor among soils. Ni toxicity varied largely among Chinese soils, and this variation can be largely explained by soil parameters. Leaching-impacted soil solution compositions and Ni EC50 values heavily. The impacts, however, were apparently different among soils. The results in this study can be used to develop a TBLM for Ni in Chinese soils. Furthermore, a need exists to quantitatively investigate the leaching effect on soil solution chemistry before leaching is used as a standard protocol in toxicity assays.

Leaching impacts Ni toxicity differently among soils but increases its predictability according to nitrification assay

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Do ammonia-oxidizing archaea respond to soil Cu contamination similarly asammonia-oxidizing bacteria?

Copper toxicity thresholds in Chinese soils based on substrate-induced nitrification assay

Leaching impacts Ni toxicity differently among soils but increases its predictability according to nitrification assay