Widespread Atmospheric Tellurium Contamination in Industrial and Remote Regions of Canada.

[NNadir]

The paper in the recent primary scientific literature that I will discuss in this post has the same title as the post itself. It is here:

Widespread Atmospheric Tellurium Contamination in Industrial and Remote Regions of Canada. (Jane Kirk et al, Environ. Sci. Technol., 2018, 52 (11), pp 6137–6145)

The first sentence of the abstract says it all basically:

High tech applications, primarily photovoltaics, have greatly increased demand for the rare and versatile but toxic element tellurium (Te).

The introductory text from the full paper states it more completely:

Tellurium (Te) is one of rarest elements on earth with crustal abundance of 1–5 μg kg–1, which is similar to gold and platinum.(1−3) Te is used in alloy production, rubber vulcanization, and increasingly in the electronics sector, particularly in cadmium-telluride photovoltaic panels and thermoelectric devices.(2,3) The increased demand for photovoltaic panels has increased Te demand, and world production has risen from ∼100 t (t; t = 1 Mg) yr–1 in 2000 to ∼500 t yr–1 in 2010.(2,3) Concerns have thus been raised about potential environmental and human health issues as some forms of Te are highly toxic.(4−11)

By the way, if you're concerned about the tellurium in solar cells - most likely you're not because you've heard again and again and again and again and again ad nauseum that solar cells are "green" - don't be. Although the toxicology of tellurium is real, particularly in acid exposure owing to the formation of H2Te gas, it's toxicology is dwarfed by the other component of "green" solar cells, cadmium.

The authors note that a planetary "tellurium cycle" has never been investigated to their knowledge, and so they set out to begin building one so at least in Canada.

They note that in seawater, the concentration of tellurium is on the order of 5-40 nanograms per liter, which is between two and three orders of magnitude smaller than natural concentration of uranium in seawater, generally taken to be 3.4 micrograms per liter.

This is because of the formation of iron and manganese nodules which enrich tellurium by a factor of 50,000 and drop it on the seafloor.

Thus when the world runs out of tellurium, given the extremely low - and thus environmentally suspect - energy to mass ratio of solar cells, cadmium telluride solar cells will lose their "renewable" status, if in fact, they ever had one.

Don't worry, be happy. Solar cells, as I've been hearing my whole adult life - and I'm not young - will save the world: Regrettably long after I, and all the people who have informed of this happy fact with such blithe confidence, will be dead.

The authors note that natural tellurium flows exist, primarily volcanoes and weathering of rocks with riverine transport, but that their estimates of anthropogenic sources effectively doubles the size of the flow:

Anthropogenic mass flows are estimated to be dominated by coal burning (700 ± 100 t year–1 and mining activities (125 t year–1).(15) The commercial production of Te has been used to estimate the mass flow due to the mining sector.(15) Due to its scarcity, Te is not mined on its own but recovered primarily as a byproduct from the processing of Cu, with Canada, Japan, Peru, Russia, Sweden, and USA being major producers.(2−4,16,17) However, due to the low efficiency (2–4.5%)(2,18) of Te extraction from Cu ore, the estimated anthropogenic mass flow due to mining(15) is low by a factor of ≥20. While the majority (∼88%) of the Te lost during copper mining is to tailings, the second highest loss is to aerosol and gaseous products during smelting/refining.(2) If not intercepted by emission abatement systems, this waste stream emits Te into the atmosphere at a rate similar to that of refined Te produced for sale.

They then describe their means of measurement:

Here we examine Te concentration profiles in dated lake sediment cores from across Canada located near the following: base metal smelting operations (Flin Flon and Thompson MB), coal mining and burning facilities (Estevan SK), oil sands mining and upgrading (Northern AB), rural regions (central AB), and natural areas remote from human disturbance (ELA ON, Dorset ON, Kejimkujik NS). The five lakes of the Experimental Lakes Area (ELA ON) are examined in more detail to reconstruct the history of anthropogenic sourced Te deposition from 1860 to 2010. Calculated modern and natural Te flux rates are compared to literature values for Te concentration in modern precipitation and the estimated rate of Te supplied by natural sources. Catchment effects and hydrologic control on lake retention of Te are also examined.

The obtain sediment cores from the deepest parts of various Canadian Lakes, and date the cores by use of Cesium-137 (nuclear testing fallout).

The samples are microwave digested in hot aqua regia, a mixture of hydrochloric and nitric acid and analyzed using a modern Agilent 7700x ICP/MS.

The map in the paper gives a feel for the findings and the geography of the testing:




The caption:

Figure 1. Tellurium concentration profiles from lake sediment cores collected across Canada (see also Figure S1). Note that the Flin Flon smelter is a significant local point source for Te emissions. While the ELA and Dorset Ontario (ON) are remote from industry, both show major Te enrichment indicating large point source(s) must exist within the Laurentian Great Lakes basin. Sudbury ON (SB) is one major source as were the former Cu smelters of the Keweenaw Peninsula (KP) MI, USA, although others (smelters + coal plants) exist. Method detection limits are represented by the blue vertical dashed blue lines in each plot. Map modified from Natural Resources Canada 2001, Atlas of Canada (https://open.canada.ca/en/open-government-licence-canada).

Some results:

Local and Regional Sources of Atmospheric Te Contamination

Te concentrations in lake sediment were generally steady and low (<0.02—0.07 mg kg–1) in rural areas of Alberta (Battle, Pigeon; Figure 1a) and in the Athabasca Oil Sands region of Northern Alberta (both near oil sands industrial development: NE20, SW22, far from 2014-Y6A, and RAMP-271; Figure 1b). Near coal mining (post-1880) and combustion activities in Southern Saskatchewan near the city of Estevan (Figure 1c), sediment Te concentrations were only above detection limits after the advent of local, small-scale coal-fired generation (∼1910). Increased sediment Te concentrations observed after ∼1960 are coincident with the advent of larger generating facilities (950 MW).(28) Like fellow group 16 elements S and Se, Te is highly enriched in coal combustion aerosols (EF ≥ 104), particularly in the <2 μm particle fraction (EF ≥ 106).(15,29) A decline in sediment Te seen in the ∼1980s may reflect early experiments in carbon capture, facility downtime due to refurbishments, and capacity reductions due to insufficient cooling water (1988; major drought), which occurred during this period.(30) Overall, the Estevan Te record remains confounded by the high mass accumulation rates, which dilute atmospheric deposition, and incomplete characterization of the natural baseline (Figure 1c).
Near metal smelters at Flin Flon and Thompson, Manitoba anthropogenic atmospheric Te deposition is obvious (Figure 1d-g). At Flin Flon (Figure 1d), with >100-fold increases in Te concentration observed after the opening (1930) of the Cu–Zn smelter. This facility was formerly Canada’s largest Hg point source, and as seen for Hg,(19) there is a strong association between proximity to the smelter and higher sediment Te concentrations (Figure 1d, Figure S3). This is not unexpected as Te is often associated with the gold content of volcanogenic massive sulfide deposits mined near Flin Flon.(31) Moreover, world Te production is mainly a byproduct from copper refinery anode sludges,(2,3) with Flin Flon being one of the early producers of Te starting in 1935.(32) Using the method previously used for Hg,(19) we estimate the inventory of anthropogenically sourced Te deposited within a 50 km radius of the Flin Flon smelter at 72.2 t (see Figure S3) over its operational history (1930–2010). Other major copper refining centers in the world likely show similarly enhanced Te deposition surrounding them.

Twenty-five Flin Flon area mines have contributed ore containing 3.4 × 106 t of copper(33) to the smelter, yielding an emission factor of 21 g of Te atmospherically deposited near Flin Flon per t of Cu processed (72.2 t Te/3.4 × 106 t Cu = 21 g Te/t Cu). As net 1900–2010 global Cu production(34) (minus production from recycling) is 451 × 106 t, we estimate that 9,500 t of Te has been deposited near Cu smelters globally. As net global refined Te production(2) (1940–2010) is estimated at 11,000 t, Te emissions to air from Cu smelters is both a large source of Te contamination and a very large loss in potential Te production. This assumes the Flin Flon smelter process and the trace element composition of the Volcanogenic-Massive Sulfide (VMS) deposits exploited at Flin Flon are comparable to other 20th century Cu producers. This appears reasonable considering current information, which while limited indicates porphyry Cu deposits (dominant global Cu and Te source) have an equivalent Te content to VMS Cu deposits.(35)

Some measurement of the enrichment in the lake cores of various elements connected with mining:



The caption:

Figure 2. Mean Enrichment Factor (EF) averaged (±1 SD) over the post-1900 period relative to pre-1860 baseline (using Al as the normalizing cofactor excepting Hg(19)) for each of the sediment cores collected from the ELA in descending order of enrichment (for elements showing an EF > 1.2). Note that for comparison this includes such elements as Mn and Fe whose up-core enrichment is due to sediment redox processes and not to anthropogenic atmospheric metals

Average annual depositions into the Experimental Lakes Area, a remote region of Canada:



The caption:

Figure 3. Anthropogenic Te deposition at the ELA reconstructed from lake sediment cores. Sediment derived anthropogenic Te fluxes corrected for lake specific Te background (mean pre-1860 Te/Al), sediment focusing (FF), and changing sedimentation are shown in a). Average anthropogenic Te fluxes for the ELA lakes are shown in b) with uncertainty bars (±95% Confidence Intervals).

Some conclusions from the paper:

Anthropogenic releases of Te to the atmosphere have elevated Te deposition to the landscape both near and far from major metallurgical centers in central Canada and likely elsewhere in the world. Reconstructions of atmospheric Te deposition history using dated lake sediment cores are in agreement with limited independent data sources and are promising for further work, although low environmental Te abundances and associated analytical issues create some challenges, particularly for defining preindustrial Te levels. With results from the ELA, Dorset and Kejimkujik indicate that long-range atmospheric transport and deposition of Te are significant, with likely contribution from multiple distant sources. As monitoring data is absent, lake sediment core based reconstructions of fluxes and inventories of Te and other high-tech elements are crucial to understand both past and present anthropogenic loadings.

The low apparent settling velocity for Te (similar to macronutrients; C, N, and P) despite its high particulate matter affinity(10,48) implies that some process(s) are acting within the aquatic environment slowing its apparent descent, possibly significant biological Te uptake and reprocessing. While Te is normally rare in the environment, it is highly toxic for most bacteria, with effects seen at concentrations 100× lower than required to produce toxic effects for more common elements of concern (Se, Cr, Hg, and Cu).(7) As Te utilization and potential human and environmental exposure has greatly increased in the past decade and is likely to increase further, it would be prudent to acquire a better understanding of Te interactions within the environment.

I'm not sure it would be "prudent." Couldn't we just declare solar cells "green" and forget about it?

Have a nice day tomorrow.

[eppur_se_muova]

1. The high toxicity of Te towards bacteria is a bit of a surprise.

When toxicity of Te in humans is discussed, it's usually in terms of acute toxicity, where, frankly, it doesn't seem so bad. The only occupations likely to result in tellurium exposure (various aspects of metallurgy) would seem likely to result in exposure to greater amounts of selenium, arsenic, and heavy metals as well, possibly masking any effects of chronic low-level exposure to Te. It appears the dangers of chronic Cd toxicity weren't appreciated until after it had claimed a number of victims. It would be a shame for the process to repeat itself with Te when such could be prevented. To some extent, I'm skeptical that will turn out to be the case, but then I wasn't expecting the high toxicity towards bacteria, either.

[NNadir]

2. The toxicology of tellurium, as is the case with sulfur, and I believe, selenium depends...

...heavily on the chemical form.

The sulfur cogener of water, hydrogen sulfide, is very toxic, and hydrogen telluride is rather nasty, albeit not very stable in air. (Hydrogen selinide is a powerful lachrymator at low ppm levels.)

Potassium tellurate is very toxic, although several people, children, known to have ingested significant quantities and survived, possibly because it's a powerful emetic. An interesting artifact is that in these cases, the victims had a powerful odor of garlic for many months after the event.

A number of organotellurium compounds produce 100% mortality at fairly low levels in mice.

I personally made - a very long time ago - some sterically hindered phenotellerols as metal complexes. If I recall correctly - and it was a long time ago - this involved aromatic grignards reacting with elemental tellurium.

Last I looked, I'm still alive.

I don't expect that it's as toxic as the other component in the solar cells in which it is "distributed," to wit, cadmium, but I think it might well prove to be something like asbestos, a chronic toxin as opposed to an immediate toxin, a hazard to the workers who handle it.

There is some evidence that it inhibits the physiological mechanisms for the management of reactive oxidation species; if I recall correctly it may have some effect on superoxide dismutase, but I'm working from memory here.

Probably the toxicology of the element is so poorly understood because it's such a rare element, which calls into question what the word "renewable" actually mean.

I personally oppose the unrestricted distribution of products containing significant amounts of cadmium telluride, particularly since their lifetime before migrating to landfills is so short, even on a human time scale.

Cadmium selenide is only slightly less terrible. Selenium is a cool element, since it's one of those elements like copper that manages to be essential at one level and quite toxic at higher levels. It's a true "the dose makes the poison" example.

I once worked in a facility where people manufactured kilogram quantities of selenomethionine as a nutritional additive.

I generally stayed out of that lab when I could do so.