Trace elements. Geochemistry-Usually those with crustal abundance of < 100 ppm or ug/g or less

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1 The last assignment is for you to pick a paper discussing the biogeochemical cycling of a trace metal. You should provide some introduction to the metal you have chosen. You must discuss the movement or cycling between at the least 2 spheres.(atmosphere/hydrosphere/biosphere/lithosphere /anthroposphere). Trace elements Geochemistry-Usually those with crustal abundance of < 100 ppm or ug/g or less Biochemistry-micronutrients-essential at low concentrations Some toxic at higher 1

2 Trace metals Metal occurrence Natural background concentrations Concentrated by geologic processes Metal release Natural rates-mechanical and chemical weathering Exacerbated by humans Concentrating Altering the rate at which they are transported between reservoirs Altering their chemical form Changing physical and chemical environments Coal = life forms so concentrations of essential micronutrients Combustion releases As, Cd, Co, Cr, Cu, Hg, Pb, Se, V and Zn Mobilization Chemical form will influence Chemistry of the environment Redox ph Adsorbtion/absorption Toxicity and bioavailability Influenced greatly by chemical form Trace metals 2

3 Almost always + oxidation number Electrophilic Important electron donors are O, N, S Metals +1 Fantastic Website s2p3 s2p2 s2p4 Lanthanide series Actinide series 3

4 Behavior in aquatic systems Sediment /soil chemistry and properties ph Eh Solution chemistry Microbial activity Other element cycles Important factors 4

5 Donald L. Sparks Toxic Metals in the Environment: The Role of Surfaces Elements, September 2005; 1: FIGURE 1 Biogeochemical pathways and processes of metals in the critical zone. Me = metal. Tiny green blobs = metal ion; brown blobs = soil particles; orange blob = colloid. Donald L. Sparks Toxic Metals in the Environment: The Role of Surfaces Elements, September 2005; 1:

6 Water chemistry is important Particulate matter chemistry and size Table 15-6 Jacobson et al Earth System Science Volatilization Most metals low vapor pressure and unlikely to be volatilized Weathering-dust, Volcanic ash, Forest fires Exceptions Hg global Organometallic compounds-large regional distribution DMSe Methylated arsenic componds Combustion-local distribution Tetraethyl lead Particulate transport 6

7 Atmosphere Reservoir 5600 Mg Global Transport GOM Hg p Hg 0 oxidation GOM Legacy source Primary Sources Anthropogenic and Natural Local dry and wet deposition Deposition from the global atmosphere pool Lithosphere-Hydrosphere-Biosphere Reservoirs (Mg) Plants Soils x 10 6 Ocean sediments - 3 x Ocean waters x 10 5 Mercury-Hydrological Processes 7

8 Anthropogenic contribution Schuster et al ES&T Mining Volcanic sources Natural sources (background) Se, As, P, Cr, Mo, W, V Negative polyatomic ions containing oxygen Ate and ite Under most conditions the trace metals sorb onto particles Oxyanions behave differently OXYANIONs 8

9 s2p3 s2p2 s2p4 Lanthanide series Actinide series Naturally occurring element Pre-1980, not well studied Improved measuring techniques Significant to human health-toxin and curative Speciation dictates toxicity and mobility Geologic setting important for impacts Contaminated groundwater big issue Arsenic 9

10 Group 5A 5, 3, 0, -1, -3 high oxidation potential metalloid Bonding mainly covalent oxygen, sulfur Chemistry 10

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12 As ph increases more metals bound + charged bound to charged Lower ph H+ competes for binding sites Oxyanions bound at low ph due to - charge more in solution at higher ph Because OH- binding Rivers Arsenate Lakes Arsenate and Arsenite Adsorption important Speciation in water 12

13 Readily adsorbed on Fe oxides Adsorption ph, concentration and water chemistry dependent Anaerobic env with high Sulfur will be precipitated Arsenic Cycling As in organisms Plants take up Bioconcentration uncertain As in soils Reduced conditions release Phosphorus addition can cause release 13

14 Arsenic oxidation: As +3 As +5 Arsenic reduction: As +5 As +3 Detoxification Energy providing Detoxification Energy providing Alcaligenes faecalis heterotrophic arsenite-oxidizing species chemolithoautotrophic species : Sulfurospirillum arsenophilum and barnesii Anabaena oscillaroides Microbial Processing As cycling linked to other chemical cycles: Iron (Fe reduction) Manganese Sulfides (sulfide oxidation) Phosphorus Microbial activity Fe, Mn, S, N cycles ph As Human influence Redox potential Aerobic/ Anaerobic Substrate Arsenic Cycling 14

15 Consensus that arsenic in contaminated groundwaters is ultimately sourced from the host sediments Release exacerbated by humans oxidation of arsenic-rich pyrite from oxygen intrusion following water table drawdown the input of phosphate from irrigated fields and its competitive adsorption led to the desorption of arsenic microbiologically mediated reductive dissolution of arsenic-rich hydrous iron oxides Ground water issue Naturally occurrence of As in groundwater of the US 15

16 Not a whole lot of data on releases Health risks minimal when compared with other heavy metals (Callender, 2004) Essential Not clear cases of over exposures Atomic number 30 and is divalent in all forms Zinc chemistry Galvanized pipes puts in waters By far the largest emissions to the air are from metal smelting and burning fossil fuels t in 1990s Ore is ZnS Major areas are Canada, Soviet Union, Australia, USA, Peru Other sources waste incineration 8000t rubber tire wear 8300 t Fossil fuels 1000 t Fertilizer production 100 t Anthropogenic Zn 16

17 Lead and Zinc emissions Figure 9 treatise 17

18 urban surburban Figure 7 Treatise Wu and Boyle GCA 1997 Ocean reference (CH3CH2)4Pb + 13 O2 8 CO H2O + Pb 2 Pb + O2 2 PbO Define tetraethyl lead 18

19 Swedish sediment varve EST v33 no Argue that Pb Cu and other heavy metal contamination occurred prior to industrial revolution Lead pollution Figure 1 Location of studied lakes in Sweden. The distance between Koltjrn and Grnstjrn is about 220 km. Published in: Maja-Lena Brnnvall; Richard Bindler; Ingemar Renberg; Published in: Ove Emteryd; Published in: Jerzy Bartnicki; Published in: Kjell Billstrm; Environ. Sci. Technol. 1999, 33, DOI: /es990279n Copyright 1999 American Chemical Society 19

20 Lows due to human inputs Gk and roman Pop growth mining expansion Plague Metal resource use peaked Concentration increases due to human inputs Figure 2 206Pb/207Pb isotope ratios and pollution lead concentrations in sediment cores from four northern Swedish lakes with annually laminated sediments. Results are plotted on a calendar time-scale obtained by counting of the annual laminations (varves). In Norrtjrnsjn the time-scale must be considered a floating chronology because of a disturbance in the varve record in the near surface sediment, and, therefore here, the results are matched to the other lakes using the lead isotope curves. Note, scale changes on the time axis. Published in: Maja-Lena Brnnvall; Richard Bindler; Ingemar Renberg; Published in: Ove Emteryd; Published in: Jerzy Bartnicki; Published in: Kjell Billstrm; Environ. Sci. Technol. 1999, 33, DOI: /es990279n Copyright 1999 American Chemical Society Heavy metal mobilization based on Ice core sampling Table 7. Heavy metal deposition fluxes at Summit, Central Greenland Age Pb Zn Cd Cu BP s 1970s Source: Candelone et al. (1995).All values are in picograms per cm 2 per year. 20

21 Fate driven by chemistry of the system and resulting chemical form Humans increase overall rate of cycling Local and regional impacts 21