ARE WE SOMETIMES TOO HEAVY ON HEAVY METALS? Robert van de Graaff, PhD van de Graaff & Associates Pty Ltd
Background to this talk • All examples are taken from my practice as a consulting soil scientist • In all cases the Environmental Assessors were concerned about real contamination and health risks due to official EPA- ANZECC-NHMRC-NEPM concentration thresholds being exceeded • There was hardly ever any real risk
Field Examples • 1. Barium panic stopping residential development near Melbourne • 2. Heavy metal accumulation in the 120 year old Sewage Farm, at Werribee near Melbourne • 3. Arsenic panic at future Melbourne Museum site • 4. Miscellaneous: chromium perceived problems • 5. Lead contamination at Ardeer battery recycling plant • 6. Lead contamination at Sandringham battery recycling plant
First let us have a look at vertical differentiation of soil profiles Duplex profile in which the topsoil Profile developed on sand over long has lost clay and iron, but iron time in moist climate. A “ spodosol ” nodules may have accumulated at the where humus and the iron has moved boundary and settled out deeper down
More common soil profiles Kinglake Plateau: Iron has been Iron concretions “buckshot” at the retained in a “fossil” soil, coating all boundary between seasonally the soil particles. Soil formed in wet waterlogged loamy topsoil and clay tropical climate subsoil. A “contemporary” soil profile in outer Eastern Melbourne
Melbourne’s drinking water under severe threat!!!! The Sugarloaf Reservoir from the air
On the beaches we find that wave action has washed out ferruginous gravels “buckshot” that belong to these soils
Chemical composition of the gravels Total (1 st rows) & TCLP Leachable (Last rows) mg/kg (except Fe in %) and mg/L As Cd Cr Co Cu Fe Pb Mn M Ni Se Sn Zn o 160 <0.5 150 8.5 18 19 42 78 <1 34 <2 <10 38 0 % As Cd Cr Co Cu Fe Pb Mn M Ni Se Sn Zn o < < < < < < < < < < 0.02 0.05 0.05 0.05 0.05 0.05 0.13 0.5 0.05 0.02 0.5 0.63 0.38
The beach gravel by Victorian EPA standards is a contaminated soil • But, Melbourne drinking water has negligible As, Cr and Mn. EPA soil classification standards are not able to provide realistic safety guidelines as they do not consider geochemical behaviour
Ironstone and bauxite, the last surviving dregs of chemical weathering Bauxite cap rock on left is a mixture Heavy metals locked up in laterite of Al(OH) 3 with ferruginous and cap rock are environmentally inert; clay impurities; Laterite or ferricrete e.g. nickel laterite cap rock on right
Soil profiles on clay parent materials A “cracking clay” formed from basalt A “red - brown earth” missing its in a relatively dry climate . Lime has topsoil, belongs in relatively dry accumulated at the base climate. Whitish layer has lime
Soil Eh and pH effects on metal speciation Normal range of soil pH and redox potential, Eh Speciation of iron
Iron oxides and hydroxides have different colours depending on mineralogy, e.g.: Goethite: α -FeO(OH) Hematite: α -Fe 2 O 3 Magnetite: FeFe 2 O 4 Ferrihydrite: Fe 10 O 15 .9H 2 O Maghemite: γ -Fe 2 O 3 Lepidocrocite: γ -FeO(OH) Courtesy Rob Fitzpatrick (CSIRO)
Gley colours and mottles in subsoils of very poorly drained soils Soil profile in a drained peat swamp, Detail of soil mottling and gleying: with grey “reduced” colour goethite is mustard yellow, hematite brick red
Munsell Color Charts – a means to standardise colour descriptions Soil colour – a means to estimate oxidation / reduction status of the soil The more red the soil, the better is its oxidation status, i.e. its natural drainage Complete lack of soil colour mottles, i.e. a uniformity of brown and reddish colours, the better its drainage status
Soil changes in relation to natural drainage regime in the landscape ► Differences in soil morphology are recognised as distinct soils ► Soil maps are made based on these distinct profiles Bath – the best drained soil profile is well oxidised throughout, whole coloured in Bir Mardin – has mottles more in Bg (B gley) due to reduction Volusia – has bleached A2 due to seasonal waterlogging Chippewa – G horizons are grey and bluish, few mottles
Effects of climate – water balance between rainfall and evaporation This transect covers soils developed on wind-blown glacial dust since the end of the last Ice Age (≈ 20,000 yrs) From west to east rainfall increases and evaporation decreases Percolating rain water dissolves calcium carbonate and moves it down the profile When plants take up water, the soil solution becomes saturated and calcium carbonate precipitates out. Gypsum is more soluble and precipitates further down
Slightly elevated Barium concentrations hold up residential development in Deer Park, Vic., and cost heaps • The soil : heavy clay soil profile developed from basalt in relatively dry climate; all these soils have illuvial CaCO 3 horizons and increasing pH with depth • The problem : “high” Ba stops the Environmental Auditor from saying the site is safe for residential use. • The economics : Developer has to pay interest on borrowed money of $A 40,000 per month, he says
What did we do? • We assumed Ba would be as SO 4 or CO 3 • We assumed BaSO 4 or BaCO 3 would behave just like CaCO 3 in illuvial processes • Sample two pits in intervals of 10 cm as far down as bedrock • Determine depth functions of pH, EC, exchangeable Na, water soluble SO 4 and Total and Leachable Ba
What did we notice and consider in the Environmental Assessor’s report? • All elevated Ba always in samples taken at 0.5 and 1.0 m depth, never at 0-0.1 m (these are prescribed sampling depths and followed by Assessors as per cookery book!) • Past land use only grazing for sheep or cattle • Therefore living plants and animals are part of the geochemistry • Therefore there must be proteins, thus sulphur, and thus SO 4 in the system
Seven offending sampling sites having “high” barium in the soil
Sampling two pits at Deer Park every 10 cm shows barium bulges at about same depth as lime Barium in HCl 0 20 40 60 80 100 120 140 160 180 200 0 10 20 Site #76 Site #104 30 40 Depth (cm) 50 60 70 80 90 100
The soil as a chromatogram Cracking clay on basalt at Deer Park, Vic. pH Electiral Conductivity 0 0 -10 -10 6 7 8 9 10 0 500 1000 1500 -20 -20 -30 -30 depth (cm) depth (cm) -40 -40 Site #76 Site #76 -50 -50 Site #104 Site #104 -60 -60 -70 -70 -80 -80 -90 -90 -100 -100 Soluble Sulphate Ba (ppm in HCl) 0 0 -10 0 1000 2000 3000 4000 -10 0.000 0.500 1.000 -20 -20 -30 -30 depth (cm) depth (cm) -40 -40 Site #76 Site #76 -50 -50 -60 Site #104 Site #104 -60 -70 -70 -80 -80 -90 -90 -100 -100
Risk assessment must rely on solubility and bio-availability of barium What is the concentration of SO 4 -2 ??
Molar concentrations of water soluble sulphate in the soil exceed that of leachable barium by factors of 10 5 Barium in these soils is inert and harmless
Long Term Effects of Municipal Sewage on Soils and Pastures at Werribee Sewage Farm Environmental Science and Health (Part A), vol. 37(4), 745-757, 2002 Robert H.M. van de Graaff, Helen C. Suter, Sophy B. Lawes
Site Information • Commenced 1897 • Size 10,900 ha • Annual Rainfall 500-550 mm • Annual Evaporation 1,400 mm • Weekly Irrigation Flow 1,743 ML • Average Irrigation Application 11.2 ML/ha.year
Soils of the Werribee Farm • Basalt and alluvial basaltic and sedimentary parent material • Texture contrast soils (Duplex soils) – Medium to heavy clay subsoils, high shrink swell • Free CaCO 3 at 30 cm depth • pH 5-7 (surface) to 8-9 (subsoil)
Disposal of Sewage • Treatment in Lagoons and Discharge to Bay 46% • No Treatment and Irrigation 54%
Table 1. Mean Heavy Metal and Total P content (mg/L) in raw sewage and annual loading to soil by irrigation kg/ha (1) and moles/ha (2) Cd Cr Cu Fe Hg Ni Pb Zn Total P Raw 0.11 0.59 0.25 2.28 0.002 0.09 0.22 0.77 10.8 sewage (mg/L) Annual 1.77 9.45 4.07 36.71 0.32 1.45 3.51 12.40 174 Loading (1) Annual 15.8 181.7 64.1 1.6 24.7 16.9 189.7 loading 657.3 5615 (2)
Heavy Metal Transfer Soil to pasture to animal tissue Note: Zn is essential micro-nutrient; Pb is not Cr-irrigated Cr-non irrigated 300 Pb-irrigated Pb-non irrigated 240 250 Metal (mg/kg) Zn-irrigated Zn-non irrigated 200 180 171 155 139 150 125 100 50 45 30 15 1.12 0.93 0.07 12 10 3.4 2.3 9 0 0 Soil Pasture Liver Data taken from Evans et al. (1978) Heavy Metal Accumulation in Soil Irrigated by Sewage and Effect in Plant-Animal Systems (Figure 3).
Heavy Metal Transfer Soil to pasture to animal tissue Note: Cu is essential micro-nutrient, Ni is not Cu-irrigated Cu-non irrigated 50 47 44 Ni-irrigated Ni-non irrigated Metal (mg/kg) 40 36 30 22 20 17 11 11 10 6.3 5.1 1.9 0 0 0 Soil Pasture Liver Data taken from Evans et al. (1978) Heavy Metal Accumulation in Soil Irrigated by Sewage and Effect in Plant-Animal Systems (Figure 3).
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