Extended abstract.Kris Broos, Michael Warne, Mike McLaughli

Broos, K.

McLaughlin, M.

Warne, M.

Adelaide Research &amp; Scholarship

What Happens After the First Shock? Temporal Changes in Microbial ECx-values in Metal Contaminated Field Trials  Kris Broos, Michael Warne, Mike McLaughlin  Centre for Environmental Contaminants Research, CSIRO Land and Water, PMB 2, Adelaide, SA 5064, AUSTRALIA (kris.broos@csiro.au)   INTRODUCTION Elevated metal concentrations in soils can disturb soil microbial processes. Several studies have concluded that soil microorganisms are more sensitive to elevated metal concentrations than other terrestrial organisms (e.g. Giller et al., 1998). Due to their essential role in soil nutrient cycling, it is argued that microorganisms should be protected. Nevertheless, maximum permitted concentrations of contaminants in soil are often derived without considering soil microbial endpoints, or, when they are considered, the data are often based on laboratory experiments where soils are spiked with metal salts. Due to salt-induced changes in metal chemistry, some negative ecotoxic effects can be measured immediately, but adverse effects may disappear fairly rapidly over time under field conditions. Other effects, such as death and extinction of specific microbial species (and therefore loss of specific soil functions), may occur slowly in the field, and are not detected during short term laboratory experiments (Giller et al., 1999).  METHODS Soils from 8 experimental field sites of the Australian National Biosolids Research Program (NBRP) were used to analyse the effect of Cu and Zn salts on both Substrate Induced Nitrification (SIN), that assesses specific microbial functionality, and Substrate Induced Respiration (SIR), that assesses total microbial population activity. Soil samples were taken immediately after addition of metal salts (T0) and after one cropping season, approximately 8 months later (T1). To measure SIN, a source of NH4 was added to the soils and the quantity of nitrate formed after 28 days was measured (OECD, 2000). Results were expressed as the % of substrate (NH4-N) utilized after 28 days. The SIR rate was measured based on the OECD guidelines (OECD, 2000) with some modifications. The respiration rate (CO2-C/g soil/h) during a 6-hour incubation experiment was measured after addition of 14C-labelled glucose (5 mg C/g dry soil).   RESULTS AND DISCUSSION Result show that the SIR EC50 values increased with time or were not significantly different at T1 compared to T0 for both Cu and Zn (Table 1). In more than half of the fields, it is not possible to detect an EC50 value one cropping season after metal addition.  In the majority of cases the SIN EC50 values for Cu and Zn exhibited the same trend as the SIR data (Table 2). However, in 2 of the 8 fields the toxicity of Cu significantly increased (lower EC50). The values presented in Tables 1 - 2 are based on total metal concentrations, and only show EC50 values, but analyses are also being conducted on added metal concentrations, for both EC50 and EC20 values and will be reported during the conference. Chemical measurements of metal availability (soil solution metals and CaCl2 extractable metals) will be taken into account to verify if 1) the exposure of the microbes to the metals changes over time or 2) microbial populations develop metal tolerance. Furthermore, the influence of acidification and increasing ionic strength due to metal salt addition will be discussed. This dataset links short term metal toxicity at T0 (analogous to short term laboratory experiments) with toxicity in field conditions (T1) and may potentially provide some factors for extrapolating thresholds derived by standardized tests into more environmentally relevant thresholds in the field.    Table 1.  EC50-values of substrate induced respiration (SIR) for Cu and Zn immediately after application (T0) and after one cropping season (T1).  Field Site Total Cu (mg/kg)  Total Zn (mg/kg)  T0 T1 significance  T0 T1 significance Tintinara 877 2742 *2  2910 2155 ns Spalding 413 766 ns3  2090 14439 ns Avon 1207 >mc1 *  2759 >mc * Cecil Plains 2341 >mc *  4946 >mc * Kingaroy 2176 1839 ns  > >mc ns  Bundaberg 699 >mc *  798 no effect * Flat Paddock 465 1537 ns  991 >mc * Night Paddock 1402 >mc *  2982 no effect * 1 calculated EC50 value greater than maximum concentration  2 EC50 values significantly different (non overlapping 95% confidence intervals) 3 EC50 values not significantly different  Table 2.  EC50-values of substrate induced nitrification (SIN) for Cu and Zn immediately after application (T0) and after one cropping season (T1).  Field Site Total Cu (mg/kg)  Total Zn (mg/kg)  T0 T1 significance  T0 T1 significance Tintinara 726 623 ns3  528 2994 ns Spalding 1245 836 *2  1011 1027 ns Avon no effect no effect ns  no effect no effect ns Cecil Plains 1972 no effect *  1256 no effect * Kingaroy 744 1646 *  936 >mc1 * Bundaberg 212 479 *  201 426 ns Flat Paddock 171 341 *  221 476 * Night Paddock 985 445 *  1621 736 ns 1 calculated EC50 value greater than maximum concentration  2 EC50 values significantly different (non overlapping 95% confidence intervals) 3 EC50 values not significantly different   ACKNOWLEDGEMENTS The authors would like to acknowledge all members of the NBRP team and to the industries supporting NBRP research. Thanks also to Ian Oliver for helpful discussions.  REFERENCES OECD, (2000) OECD Guidelines for testing of chemicals. Soil Microorganisms: Nitrogen transformation test and Carbon transformation test. Paris. OECD. Giller, K.E., Witter, E., McGrath, S.P. (1998) Toxicity of heavy metals to microorganisms and microbial processes in agricultural soils: a review. Soil Biol. Biochem. 30: 1389-1414. Giller, K.E., Witter, E., McGrath, S.P. (1999) Assessing risks of heavy metal toxicity in agricultural soils: Do microbes matter? Hum. Ecol. Risk Asses. 5: 683-689.  

What Happens after the First Shock? Temporal changes in microbial ecx-values in metal contaminated field trials

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/41445/1/McLaughlin_552_final.pdf

What Happens after the First Shock? Temporal changes in microbial ecx-values in metal contaminated field trials

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Adelaide Research & Scholarship

What Happens after the First Shock? Temporal changes in microbial ecx-values in metal contaminated field trials

Abstract

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Adelaide Research &amp; Scholarship

Adelaide Research & Scholarship