Emissions of heavy metals (Mercury, Lead, Cadmium and other metals)

Heavy metals differ significantly in their properties and ability to long-range atmospheric transport. In particular, mercury is well known as a global scale pollutant with distinct ability to intercontinental transport. On the other hand, such particle bound heavy metals as lead and cadmium are mostly transported regionally. Therefore, mercury has the first priority for modeling on a global scale and requires global emissions data. Nevertheless, in many cases modeling other heavy metals also requires emissions data covering territories wider than the region of the primary interest. For example, lead and cadmium pollution levels in the EMEP countries and, in particular, in the EECCA countries can be affected by emission sources located in neighboring non-EMEP countries of Northern Africa, Meddle East, Eastern and Southern Asia.

Although, there are detailed heavy metal anthropogenic emissions inventories developed for a number of regions (e.g. Europe, North America), global emission datasets are quite rare. Table contains characteristics of available global emission datasets and inventories for some heavy metals. Global spatially resolved data on mercury emission are available for a number of years (1990, 1995, 2000, 2005). The only gridded emission dataset for lead relates to 1990. The lead emissions inventory has been updated for mid-nineties but these data have no spatial distribution. Only aggregated emission estimates without spatial distribution of emission sources are available for cadmium and relate to mid-nineties.

 

Chemical Period of time Global emissions, t/y Spatial resolution Dataset location Reference

 Mercury

1990 2 144 1º—x1º CGEIC  CGEIC website
1995 2 317 0.5º—x0.5º

 

AMAP

 Pacyna et al., 2003
2000 2 190 0.5º—x0.5º  Pacyna et al., 2006
2005 1930 0.5º—x0.5º  AMAP/UNEP, 2008
2010 1960 0.5º—x0.5º  AMAP/UNEP, 2013

 Lead

1989 167 889 - 206 435  1º—x1º CGEIC  Pacyna et al., 1995
1995 119 259 n/a n/a  Pacyna and Pacyna, 2001
 Cadmium 1995 2 983 n/a n/a  Pacyna and Pacyna, 2001

 

Mercury (Hg)

First global dataset of mercury anthropogenic emissions relates to 1990 and is available at website of the Canadian Global Emissions Interpretation Centre (CGEIC). It covers the globe with spatial resolution 1ºx—1º and distinguishes emissions from point sources (power plants, smelters and other large sources with stack height and a sufficiently buoyant plume that the emissions are transported into the atmosphere above 100 m) and area sources (e.g. residential and commercial boilers, mobile sources etc.)

Later two newer global mercury emissions datasets were released for 1995, 2000, 2005, 2010. They are available at the website of the Arctic Monitoring and Assessment Programme (AMAP) and contain considerably more detailed information on mercury emissions. The datasets have spatial resolution 0.5º—x0.5º and include the following parameters:

  • Gridded anthropogenic emissions separately from point and area sources;
  • Three emission height levels (below 50 m, 50-150 m, above 150 m);
  • Speciation of mercury emissions into elemental gaseous mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (TPM).

The figure shows spatial distribution of mercury anthropogenic emissions in 2010 (g/km2/y). Areas with elevated mercury emissions correspond to highly industrialized regions: Europe, Eastern United States, Southeastern China, Japan, India and South Africa.

 

 

 

Lead (Pb)

The only global spatially resolved emissions inventory for lead relates to the year 1989 and is available at the CGEIC website. This dataset includes gridded information on lead emissions from point and area sources with spatial resolution 1º—1º. Besides, it provides low and high estimates of the emission rates based on emission factors that were assumed to be the highest and the lowest values within the emission factor ranges for a given source category. The figure shows global distribution of anthropogenic emissions of lead in 1990 (kg/km2/y). According to this inventory the most significant emission sources were located in Europe, Southeastern Asia, Mexico and South Africa. Global emission estimates varied from 168 to 206 kt/y.

The global emissions inventory for lead has been updated by Pacyna and Pacyna (2001) for mid-nineties. Estimates of lead emissions from anthropogenic sources have been revised based on new information from national experts in combination with statistical data on the consumption of raw material, industrial goods production. However, the updated inventory did not include spatial distribution of emissions. According to the inventory combustion of gasoline continued to be the major source of atmospheric emissions of lead, contributing about 74% of global emission in 1995.

 

 

Cadmium and other heavy metals

There is no spatially resolved global emission datasets available so far for cadmium and other heavy metals and metalloids (arsenic, chromium, copper, nickel, selenium and zinc). The most recent inventory for these metals includes total emission estimates for different continents and various source categories and relates to 1995 (Pacyna and Pacyna, 2001). The inventory contains estimates of heavy metal emissions from heat and power production, non-ferrous metal production, iron and steel industry, cement production and waste disposal. Emission of heavy metals from major anthropogenic source categories is presented in the Table. The estimates indicated that stationary fossil fuel combustion was the major source of chromium (69%), nickel (90%), and selenium (89%). Whereas non-ferrous metal production was the largest source of atmospheric emissions of cadmium (73%), arsenic (69%), copper (70%), and zinc (72%).

 

Source category Cd As Cr Cu Ni Se Zn
Stationary fossil fuel combustion 691 809 10 145 7 081 86 110 4 101 9 417
Non-ferrous metal production 2 171 3 457 18 071 8 878 466 40 872
Iron and steel production 64 353 2 825 142 36 7 2 118
Cement production 17 268 1 335 - 134 3 2 670
Waste disposal 40 1 124 425 621 129 24 1 933
Total 2 983 5 011 14 730 25 915 95 287 4601 57 010

 

Asia was the largest contributor to global heavy metal emissions made up 40-60% of total value. Contributions of other continents vary for different metals. Europe contributed 23% of global emissions of chromium and 21% of nickel; North America made up 24% of selenium and 22% of chromium emissions; South America was responsible for 21% of global copper emissions. The lowest contributions were made by Australia.

 

Emissions of Persistent Organic Pollutants (PCBs, HCHs, HCB, PCDD/Fs, PAHs)

A number of inventories of the global production, usage and emission for selected POPs were developed recently. The information on available inventories including the estimates of POP usage, production and emissions is presented in the table. Some of the inventories contain the data on total emissions for particular countries, their temporal variations, and gridded emission data. In particular, PCB emission inventory presents a full set of information on spatial variations of emissions on global scale and their temporal variations with annual resolution in period 1930-2100. Gridded emissions data are also available for a-HCH and y-HCH for 1980, 1990, and 2000. For other POPs the estimates of total emissions of particular countries are available. Nevertheless this information can also be used for modeling purposes. Below a description of available POP emission inventories is presented.

Chemical Use Period of time Global use/ production, kt Global emissions, kt Reference
PCDD/Fs
(as kg TEQ)
By-products 1990   50 Brzuzy and Hites, 1996
1995   10.5
8.3 - 36
UNEP, 1999
HCB Pesticide
By-product
Mid 1990   0.023
0.012 - 0.092
Bailey, 2001
Technical HCH Insecticide 1948-1997 10000   Li, 1999
Lindane Insecticide 1948-1993 720   Voldner and Li, 1995
  6000   Sang et al., 1999
1950-2000 600   Li and Vijgen, 2005
α-HCH Insecticide 1980 290 184 Li et al., 2000
1990 59 44
b-HCH Insecticide 1945-2000 850 230 Li et al., 2003
1980 36 9.8
1990 7.4 2.4
2000 - 0.066

PCBs

Various 1930-2000
and
up to 2100
1320 7.71
0.44 - 91.7
Breivik et al., 2002a
Breivik et al., 2002b
Breivik et al., 2007
PAHs By-products 2004   520 Zhang and Tao, 2008

 

PCBs

A global historical emission inventory for selected PCB congeners (22 PCB congeners) was prepared by Breivik et al. (2002a). The available data of the historical production of PCBs and the chemical composition of various technical mixtures have been compiled from the literature. Information of imports, exports and consumption, as well as restrictions on production and import has further been analyzed for individual countries. The estimates account for a reported historical global usage of approximately 1300 kt of PCBs. The results suggest that almost 97% of the global historical use of PCBs have occurred in the Northern Hemisphere (Breivik et al., 2002a).

In the second part of this study, an attempt has been made to estimate the historical anthropogenic emissions as a direct result of the widespread usage of PCBs for a period of 70 years. The historical emission of 22 PCB congeners is estimated to be between 440 and 91722 t, with 7709 as the average value (Breivik et al., 2002b). In accordance with this three emission scenario were developed, in particular, low emission, average emission, and high emission scenario. In spite of the major uncertainties, the study is considered as a first important step towards the establishment of a global PCB emission inventory with congener resolution. The importance of temperature as a key parameter in controlling and affecting both the absolute value of PCB emissions as well as the PCB emission profile is emphasized.

The third part of this study presents an update of preceding PCB emission database. This work takes into account updated information on PCB production, as well as new data on the chemical composition of various technical mixtures for which less information had been available earlier. The methodology to estimate temporal trends of PCB usage is improved. The authors have also included projected emissions up to year 2100, which can facilitate predictions of future environmental exposure. The national emission data for each of the 114 countries considered is spatially resolved on a 1º—1º grid for each congener and year, using population density as a surrogate (Breivik et al., 2007), as indicated for PCB-153 for 2000 (kg/cell/y) in the figure:

 

 

HCHs

HCH is an organochlorine insecticide employed throughout the world. It has also been used for seed protection, poultry and livestock treatment, household vector control, lumber protection, and even for rodent baits. The HCH has two main compositions: technical HCH and lindane. Lindane consists almost entirely of γ-HCH, the insecticidal form, technical HCH contains a total of eight HCH isomers, among which only the α, β, γ, δ and ε isomers are stable and commonly identified. Around 10,000 kt of technical HCH has been released to the environment between 1948 and 1997 (Li, 1999). Global gridded emission data for HCH isomers are available for a-HCH and b-HCH.

 

α-HCH

Estimations of global gridded y-HCH emissions in 1980 and 1990 resulted from the application of technical HCH were presented Li et al. (2000). The total global usage of y-HCH was estimated to be around 290 kt in 1980 and 59 kt in 1990. Total global α-HCH emissions in 1980 were 184 kt and 44 kt in 1990. In 1980 approximately 74% of the global y-HCH emissions originated in the Northern Hemisphere mid latitudes, followed by around 19% in the Northern Hemisphere tropics, while in 1990 approximately 54% of the global y-HCH emissions originated in the Northern Hemisphere tropics, followed by around 37% in the Northern Hemisphere mid latitudes. Among total global y-HCH emissions, 85% and 75% originated in Asia in 1980 and 1990, respectively (Li et al., 2000). The spatial distribution of annual emission of y-HCH for 2000 (t/cell/y) is presented in the figure.

 

 

b-HCH

Global gridded b-HCH emission inventory was prepared by Li et al. (2003). The total global usage of b-HCH between 1945 and 2000 is estimated as 850 kt, 230 kt of which was emitted to the atmosphere over the considered period of time. Usage of b-HCH was estimated to be around 36 kt in 1980 and 7.4 kt in 1990. Total b-HCH emissions in 1980 were 9.8 kt and 2.4 kt in 1990. While it is assumed that no usage of technical HCH occurred in 2000, the global b-HCH emissions during this year due to soil residues were estimated at 66 t. It has shown that the global b-HCH emissions have undergone a "southward tilt" over the time period studied as more northern countries have banned the use of technical HCH (Li et al., 2003).

 

γ-HCH

The majority of the developed countries prohibited the application of HCH in the 1970s. Lindane replaced technical HCH. The amount of global lindane usage has been estimated by a few scientists. Voldner and Li (1995) gave worldwide lindane usage between 1948 and 1993 as 720 kt, and Sang et al. (1999) suggested the global consumption of lindane should be 6,000 kt, more than 8 times as that given by Voldner and Li (1995). Global lindane use for agricultural purpose between 1950 and 2000 is estimated to be 450 kt, among which 280 kt was used in Europe, 73 kt in Asian, 64 kt in America, 29 kt in Africa, and 1 kt in Oceania countries (Li and Vijgen, 2005). Although lindane use in most European countries has been banned, the historical lindane use from 1950 to 2000 in Europe reached approximately 63% of the total global use. Global annual lindane usage was highest in the 1960s and the beginning of 1970, and has since been declining. Global use in 2000 was approximately 2 kt (2204 tons). The total global lindane usage for all purposes could be approximately 600 kt (Li and Vijgen, 2005; IHPA, 2006). The last estimate of global lindane use is less than those given by both Voldner and Li (1995) and Sang et al. (1999).

 

HCB

HCB had been actively used in industry and for agricultural purposes. HCB was first introduced in 1933 as a fungicide on the seeds of onions, sorghum and crops such as wheat, barley, oats and rye. It is believed that agricultural use of HCB dominated its emissions during the 1950s and 1960s. The peak of HCB production was the late 1970s and early 1980s worldwide. Production of HCB declined as a result of restrictions on its use. The banning of HCB for agricultural use in the 1970s removed the largest single primary source of HCB in the environment (Barber et al., 2005). Although HCB production has ceased in most countries, it is still being generated inadvertently as a by-product and/or impurity in several chemical processes, such as the manufacture of chlorinated solvents, chlorinated aromatics and pesticides (Jacoff et al., 1986). HCB can be also released to the environment by incomplete combustion and from old dumpsites.

Global emission estimate for HCB was presented in (Bailey, 2001). This study presents the information from a variety of sources of HCB emissions and gives a quantitative estimate of the global HCB emissions in the mid 1990s. The best estimates of global HCB emissions from different categories of sources are as follows: pesticides application - 6500 kg/y; manufacturing - 9500 kg/y; combustion – 7000 kg/y, including 500 kg from biomass burning. This adds up to total current HCB emissions of approximately 23,000 kg/y with an estimated range 12,000-92,000 kg/y (Bailey, 2001). The author suggests that a substantial portion of HCB measured in the atmosphere is thought to come from volatilization of y-HCB on the soil from past contamination along with unidentified sources. Globally, the magnitude of these secondary emissions is currently not known, but this is a potentially very important aspect of the current global HCB cycle (Barber et al., 2005).

To describe contemporary levels of HCB pollution experimental scenario of recent and historical global HCB emissions for the period from 1945 to 2013 was developed [Shatalov et al., 2010]. Following available information the application of HCB, largely in agricultural activities as a fungicide, was started from 1945 and reached its maximum in 1980-s. Starting from that period the agricultural use of HCB was banned in many countries world-wide resulting in considerable decrease of primary emission of HCB and the increase of relative importance of HCB re-volatilization. According to constructed scenario emissions of HCB decreased from its maximum in 1978 to 2013 by more than 400 times.

Spatial distribution of global HCB emission fluxes for 2013 is shown in the figure. The largest HCB emission fluxes took place in Southern and Eastern Asia. Releases of HCB to the atmosphere in the EMEP region were relatively lower.

 

 

PCDD/Fs

PCDD/Fs enter the environment as by-products of industrial processes. The most significant type of sources of PCDD/F emission to the atmosphere is low-temperature, incomplete incineration of chlorine-containing materials such as plastics. Other major sources include thermal processes, such as motor vehicle fuel combustion in countries where leaded fuel containing chlorine scavengers is still used, and metallurgical industries. PCDD/Fs are also trace contaminants in chlorophenoxy herbicides, PCB formulations, and chlorophenol wood preservatives (AMAP, 2004). Rough estimates of the global emissions of PCDD/Fs are available from Brzuzy and Hites (1996). The authors calculated annual global emission to approximately 50 kg TEQ for 1990. They based on assumptions that the global PCDD/F emissions from different categories of sources are as follows: waste incineration - 20 kg TEQ/y; cement kilns - 17 kg TEQ/y; manufacturing - 7 kg TEQ/y, and combustion - 6 kg TEQ/y.

In addition, an overview of available emission inventories for PCDD/Fs on global level can be found in (UNEP, 1999). This report includes estimates of PCDD/F emissions for Western Europe, Northern America (Canada and the United States). For Asian region there is only one inventory for Japan, which covers a few source categories, and the estimates for emissions from waste incinerators from South Korea. From the southern hemisphere, only Australia has estimated annual emissions. Japan and the United States were considered the largest emission sources of PCDD/Fs (4 kg TEQ/y and 2.7 kg TEQ/y, respectively). The average estimate of annual “global” PCDD/F emission is amounted to approximately 10.5 kg TEQ for 1995. The lower estimate is about 8.3 kg TEQ/y and the upper estimate is approximately 36 kg TEQ/y. The waste incineration is still the major emitter of dioxins and furans to the atmosphere with contribution to the total emission reaching almost 70 %. The majority of PCDD/PCDF emissions from this sector are due to the municipal (and to a lesser extent to the hazardous) waste incinerators located in Japan. This source sector alone is responsible for almost 34 % of the total PCDD/PCDF inventory to air from identified sources so far (UNEP, 1999).

To evaluate global transport and fate of PCDD/Fs experimental emission scenario was constructed on the basis of the information on dioxins and furans releases compiled under UNEP SC. National inventories of annual PCDD/F emissions were available for 68 countries representing the level of emissions during the recent decade (Fiedler, 2007; Fiedler et al., 2012; UNEP, 2013). Compiled inventories covered main modes of entry of emissions to the environment (the atmosphere, land, water, residues, and products), among which major releases were indicated to the atmosphere (45%). Analysis of this information, performed by Cao et al. (2013) permitted to reveal correlation between the intensity of PCDD/F emissions in the countries and their economic status. Obtained regression relationship between the national PCDD/F emissions and the data on GDP and total population of the countries was applied to estimate emissions for the other countries, for which the information on emissions was not available. Thus based on this information amount of PCDD/Fs released to the environment annually was estimated to about 80 kg TEQ. Spatial distribution of PCDD/F emissions was generated using the population density as a surrogate.

 

 

Spatial distribution of annual PCDD/F emissions to the atmosphere (top) and to soil (bottom) constructed on the basis of UNEP global PCDD/F emission inventory, ng TEQ/m2/y

 

 

PAHs

Evaluation of global emission of PAHs from about 200 countries to the atmosphere for 2004 was performed in (Zhang and Tao, 2008). According to their estimates the total global atmospheric emission of the 16 PAHs listed as the US EPA priority pollutants is accounted for 520 kt/y. Authors supposed that biomass burning including both biofuel and wildfire are dominating emission sources of PAHs with relative contributions of 57% and 17% to the total PAH emission, respectively. At the same time source profiles of individual countries varied remarkably depending on their status of development, population density and vegetation cover. The maximum annual emission of PAHs was estimated for Asia accounting for 290 kt/y (55% of the global PAH emission). The emissions of Africa, Europe, North America, South America and Oceania contributed 19%, 10%, 8%, 6% and 1.5% to the global PAH emission, respectively (Zhang and Tao, 2008).

 

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