Issue Date Author Ghanta, Madhav. Publisher SpringerOpen. Type Article. Metadata Show full item record. The quantity of ethene emitted per km driven varied greatly. This fold reduction was largely the result of emissions controls and requirements for cleaner burning fuels in the United States and Canada Environment Canada b. These data can be used to estimate tonnes of ethene potentially released in Canada, assuming that the vehicle distribution for Canada is similar to that of the Lower Fraser Valley.
This estimate will likely be high, as the older vehicles from had ethene emissions that were high compared to more modern vehicles. Canadians in light-duty vehicles under 4. This calculation resulted in a total estimated release of ethene for Canada from light-duty vehicles at tonnes in As the Canadian vehicle fleet ages the proportion of vehicles older than will drop resulting in substantial decreases in the amount of ethene released by Canadian vehicles.
For the purpose of this assessment, the original site types were recategorized for clarity. Based on this information, the NPRI lists 1 facilities that reported releasing tonnes and recycling tonnes in Alberta of ethene in Environment Canada ; Table 3. Releases of ethene in this report are considered from industrial operations generally, rather than from specific industries, unless otherwise noted.
The trend in actual releases not counting tonnes sent for recycling or spillage of ethene reported to the NPRI has been decreasing significantly so that releases to the environment in are less than half of that reported for see Table 4 Environment Canada All releases in this report are expected to be to air since none have been identified to soil, water or sediment. Ethene from anthropogenic sources is almost always released to air as it is a gas at environmental temperatures.
Ethene is not expected to be released to soil, sediment or water thus no exposure is expected and these routes were not investigated. Thus, the most probable route of ethene exposure is through contact with air e. Physical removal of ethene from the atmosphere can occur through wet deposition; however, this process is negligible due to ethene's short half-life in the atmosphere and moderate water solubility.
Certain evidence suggests that some ethene removal is facilitated by soil bacteria and fungi; however, as with wet deposition this process is not as efficient as the atmospheric chemical reactions which are 30 to 60 times more effective Alberta Environment Experimental and modelled data concerning the biodegradation and persistence of ethene in different environmental media are presented in Table 6.
Modelled biodegradation values for ethene indicate that the half-life is less than days in water and soil. Howard et al. Ethene is readily oxidized in the atmosphere with a theoretical global residence time in the troposphere ranging from 2 to 4 days.
There are, however, numerous chemical reactions associated with the breakdown of ethene which may decrease its half-life to just a few hours Sawada and Totsuka The oxidation of ethene can generate nitrogen dioxide NO2 which can later form ozone.
In a report for the California Air Resources Board, Carter developed a complex model based on years of air chamber tests to determine the impacts of chemicals on O3 and NO3 formation.
In their report are relative reactivities based on effects of chemicals on the maximum 8-hour average ozone concentration in 39 cities across the continental USA. Under these test conditions Carter calculated that ethene generated an average of 9 grams O3 for each gram added to the atmosphere Carter Ethene is used as the criterion against which other chemicals are measured for tropospheric ozone formation.
Prinn et al. This gives an atmospheric half-life of 1. Other estimates of the oxidative half-life in air were 1. Ethene has an expected reactive half-life in air of 1. Using an extrapolation ratio of for water:soil:sediment biodegradation half-lives Boethling et al. Therefore, the half-life in soil is 1 - 28 days and in sediment is 4 - days. As calculated using the extrapolation ratio for degradation in water : soil : sediment from Boethling et al.
Return to footnote Table 5 [a] referrer. The long-range transport potential of ethene in air was estimated using the TaPL3 model v3.
The characteristic travel distance CTD of the substance calculated by the model is km. According to Beyer et al. There are no empirical data characterizing BCFs or BAFs for ethene; however, it is expected that bioaccumulation and bioconcentration of ethene in aquatic systems is limited due to its low log K ow of 1.
The BAF model is usually preferred, as it represents uptake of chemicals from water and the diet however, no diet contribution is expected thus BAF was not considered. Based on the above information ethene is neither persistent nor bioaccumulative in the environment. The only pathway of release known in Canada is through releases to air and in conjunction with the degradation information presented in Table 6, ethene is unlikely to be found in water, sediment or soil at concentrations greater than what is naturally present in the environment.
Consequently, only air concentrations are reported in this section. Although environmental ethene concentrations are dependent on both natural and anthropogenic sources, the consistently highest concentrations are measured in urban areas due to the combustion of fuel, coal and natural gas by vehicles and industrial facilities. Industrial facilities may also release ethene through production processes. The range of concentrations in Edmonton was 0. Air concentration data from forty-nine National Air Pollution Surveillance NAPS air monitoring network sites Environment Canada b for the years to were selected and analyzed.
Data from some monitoring stations were not included in the ecological assessment as not all locations were considered relevant. Sampling periods were either 4 hours or 24 hours long depending on the site and other parameters many sites were sampled for four hours. All sites were re-classified from their original designation as remote background , rural, or urban based on their respective locations in Canada and proximity to cities and townships urban , agricultural and semi-developed areas rural or areas that were considered minimally impacted remote.
Differences among these three types of sites were investigated using average values from each site in an Analysis of Variance test ANOVA followed by pair-wise comparisons using the Tukey test Minitab There was a statistically significant difference among groups P less than 0.
Table 6 shows the air concentrations at the three different site types for two periods, and The concentration of ethene in urban areas was considerably higher than that in background and rural areas.
This was likely due to vehicle emissions and the presence of industrial sources of ethene. While two of the NAPS monitoring stations are near industrial sources of pollution, the remainder are not, so a statistic analysis of the co-occurrence of ethene and industries was not possible.
The few reported monitoring programs at petrochemical facilities reported highly variable concentrations of ethene. One facility in Alberta detected a range of 2. Areas close to such facilities will receive higher peak values of ethene. The highest daily concentration Table 6 from recent air monitoring in an urban setting was This site has several ethene producing or using industries and has highly variable air concentrations of ethene.
The average concentration of ethene in urban areas in Canada has decreased over a period of 10 years from The average from to was 2. Between and , the highest daily concentration at rural sites Table 6 across Canada was 7. The average concentration of ethene at rural monitoring locations has increased slightly from 0. The highest daily concentration at remote sites across Canada between and Table 6 was 1.
The average concentration of ethene was 0. It can be reasonably stated that ethene concentrations in remote regions of Canada are very low and have not changed significantly in the recent past nor is ethene being transported over long ranges from sites with higher concentrations. Table 6. Daily air concentration data at different types of sites for the periods, and Environment Canada Canadian data on the release of ethene from industrial sites was provided by both industry and by regional environmental associations, representing monitoring at either only industrial fence lines industry submissions or both industrial fence lines and further afield environmental association monitoring.
The annual average concentration reported by industry ranges from 1. Regional monitoring of ethene was conducted by an environmental association in the Sarnia-Lambton area of Ontario; this region contains several industrial sources of ethene as well as vehicle and urban emissions including from a major provincial highway.
Hourly data from January to December in this urbanized, industrial area were provided, and 3-day averages were calculated in order to compare against industry data. Data from five monitoring stations were provided. Three monitoring stations were at industrial fence lines while two were further afield. The two furthest stations were approximately 13 km apart.
Upon further investigation, this value was caused by an event lasting only 6 hours in the early morning of August 3, , when ethene concentrations spiked across all five monitoring stations in the region. The cause of this increase is not known but was atypical. Given that this event was isolated, was of very short duration and the ethene concentrations returned to their prior values, this data was removed from consideration in the risk assessment.
Ethene is produced and used as a hormone in higher plants, as such it has effects on many growth and developmental processes depending on concentration, growth stage during exposure, and length of exposure. Many growth effects are reversible if they do not continue for very long; developmental processes however, are often not reversible if the process has a short time-frame within which to occur, such as flower development. Ethene exposure promotes early leaf abscission drop and epinastic growth leaf curling , it can stunt root growth, and it also affects developmental processes involved in reproduction such as flower bud formation and development, fruit ripening, and extent of flowering Blankenship and Kemble ; Alberta Environment The impact of effects on flowering is a reduction in the ability to reproduce; the effects on roots and leaves can lead to stunted growth.
However, because ethene is a plant hormone not all effects are negative. The agriculture industry exploits these effects by using ethene to ripen green-picked fruit and to delay flower opening during transport to markets. At air concentrations between 5. Some cereals, such as barley and oats, appear to be highly sensitive to ethene at air concentrations as low as Tomatoes show slight curling of leaves at Goeschl and Kays note that the stage of development can influence the type of response to ethene, as can the length of exposure Dueck et al.
Some authors suggest that the lack of a recovery period is why plants in experiments appear to be more sensitive to ethene than do plants exposed in the environment where exposure from industrial releases is not constant and is often of short duration Tonneijck et al.
Similar exposure during dark hours did not affect photosynthesis. Potatoes that experienced reductions in photosynthesis were found to recover within 48 h Dueck et al. It is difficult to predict the response of a particular species to exogenous ethene; closely related species can respond differently, and even agronomic cultivars can respond differently to ethene.
In barley Hordeum vulgare the cultivar "Harrington" was very sensitive to ethene while the cultivar "AC Lacombe" was not Archambault et al. Rajala et al. Fiorani et al. This response was based more on growth habit than any other apparent attribute of the plants. This is based on a log-log relationship pooling all short and long-term data from Archambault and Li Return to footnote Table 7a [a] referrer. Archambault and Li developed a dose-response function to determine a threshold concentration 5.
Harrington, the most sensitive cultivar in the study. Archambault and Li further determined from the dose response curve that a concentration of Thus 5. However, it should be noted that Archambault and Li tested two cultivars of barley and used the more sensitive cultivar cv. Harrington as it showed heightened sensitivity to ethene compared to the other cultivar cv. AC Lacombe. Thus both CTVs reflect not only a sensitive species, but a sensitive cultivar within that species.
Additionally, studies that looked at the effects of epinasty were not considered relevant as epinasty is not considered a harmful effect, but merely an indicator of the presence of elevated levels of ethene.
No effects data were found on invertebrates or birds, which are most likely to be exposed to ethene. The concentrations of ethene tested within the following mammalian studies are considerably higher than concentrations expected in the Canadian environment. Exposure to concentrations of ethene that are considered environmentally relevant did not lead to toxic effects after exposure to rats see Appendix 2 for further details. Ethene is not expected to be released to water and thus no water exposure is expected.
No adequate empirical toxicity studies on aquatic species were found. Considering that ethene is not expected to be released to water these concentrations are highly unlikely over such periods of time such that the model results are not considered relevant to Canadian release scenarios of ethene. The approach taken for this assessment was to examine the available scientific information and develop conclusions based on a weight-of-evidence approach and using precaution as required under CEPA. Lines of evidence considered include information on the environmental sources, fate, persistence, bioaccumulation potential, and ecotoxicity of the substance.
Risk quotient RQ analyses, which integrate known or potential exposures with known or potential adverse ecological effects, were also performed for ethene. Only air exposure scenarios were considered in this assessment due to the low exposure potential to ethene in water, soil and sediment.
Terrestrial plants were selected as the most sensitive ecological receptors to ethene in this media. To estimate the risk to Canadian ecosystems, four exposure scenarios were developed for short-term and long-term exposure regimes with their respective predicted environmental concentrations PEC.
Based on an initial analysis of air monitoring data from across Canada, rural and urban locations were identified as being potentially at risk from ethene emissions, likely from automotive engine emissions. Air monitoring data were used to develop averaged short-term and long-term concentrations for rural and urban areas. Industrial emissions were also assessed using two scenarios under short-term and long-term exposure regimes.
Industrial and regional monitoring data were used to develop scenarios for a realistic worst-case using the Sarnia-Lambton monitoring data which combines both industrial and ambient concentrations of ethene, and an average case using the annual average of the release data for all industrial facilities in Canada. Two exposure scenarios were developed to determine if the ambient ethene concentrations in rural and urban Canada pose a hazard to vegetation over short- and long-terms.
Each scenario reflects ambient monitoring data from either rural or urban sites across Canada compared against short- and long-term thresholds for potential negative impacts to vegetation.
These values reflect average annual ethene releases from across Canada. Based on air concentrations measured at sites across Canada from to , PECs for long-term ambient concentration exposure scenarios were based on the mean daily concentrations from April - September of 0. For short-term ambient exposure scenarios, the maximum concentrations of 3.
Both the average and the worst-case scenarios were compared against short and long-term exposure thresholds to plants. A long-term exposure PEC of 3. PECs for the industrial realistic worst case scenario were also determined based on regional monitoring data the Sarnia-Lambton area of Ontario. A long-term exposure PEC of 5. Environment Canada Short-term concentrations reflect daily maximums while long-term concentrations reflect the average of daily concentrations. Return to footnote Table 8 [a] referrer.
Return to footnote Table 8 [b] referrer. Return to footnote Table 8 [c] referrer. An assessment factor of one was applied for terrestrial plants as the available data spanned a range of species, including sensitive species. Toxicity data included both laboratory and field studies; as laboratory studies are more sensitive to ethene than field exposures due to their continuous exposure, no assessment factor was considered necessary to take into account laboratory to field variability. CTVs typically represented the lowest ecotoxicity value from an available and acceptable data set.
For this assessment, two CTVs were chosen to represent terrestrial plants in a short-term and a long-term exposure scenario. A CTV of 5. The RQs indicate that ambient concentrations of ethene do not pose short- or long-term risks to plants in urban areas or rural areas.
Table 10 presents the summary of the risk quotient calculations for industrial releases. The realistic worst case for industrial releases generates an RQ of 2. The average case for industrial releases generates an RQ of 0. These risk quotient analyses indicate that ethene could pose short-term risks to local terrestrial vegetation from worst case industrial facility releases as indicated by a risk quotient of 1 or greater.
These reflect annual concentrations and as such are not restricted to April - September. Return to footnote Table 10 [a] referrer. Return to footnote Table 10 [b] referrer. Only the data submitted by SLEA were suitable for this calculation.
A total of 14 incidents in the entire dataset had 3-day averages above this threshold and of these days, only 7 exceedances occurred between April and September representing 0. Exceedances occurred only at sites within close proximity to the source i. This represents an approximate average of one short-term occurrence per year near ethene-releasing industrial sites of a sufficient concentration that may cause harm to plants.
For the realistic worst case industrial scenario, a risk quotient of 1 was obtained using a PNEC of 5. Harrington , the most sensitive cultivar of a sensitive species tested Archambault and Li, At this concentration no effects on plants were found, regardless of exposure time, as Archambault and Li considered this value equivalent to the background, or control, concentration.
Given this, the concentration of 5. In this scenario, it is assumed that plants will be exposed to a continuous concentration of ethene, which, based on monitoring data, is not the case. Ethene concentrations vary considerably both with time of day as well as with time of year. It is likely that concentrations of ethene would not be maintained at the highest levels for long periods of time, thus allowing most plants to recover.
Because of these factors, the industrial worst-case scenario is not expected to cause long-term impacts on plants. Atmospheric exposure of plants to ethene is heavily dependent on a number of external factors.
Laboratory studies frequently expose plants to continuous sources of ethene while environmental exposure is far more variable, affected by such things as wind, weather and variability in stack releases over the course of a year, and often not sustained for long periods of time.
Given that exposure will be discontinuous, plants may be able to recover from ethene exposure prior to being re-exposed. The propensity for recovery or reversibility of effects however is dependent upon concentration and duration of exposure, as well as the nature and the extent of the effects and on the species of plants, thus making the impact of environmental ethene difficult to predict.
Tonneijck et al. Despite these elevated levels, plant yield in the surrounding area was unaffected by ethene emission. Plants closer than m to the source of emissions did show loss of flowers and decreases to the mean growth rate. Dueck et al.
They found that potato leaves recovered fully after 12 hours of exposure and 3 days of recovery time. Overall, there was a decrease in the number of flower clusters; however, potato yield including size or frequency of misformed potatoes was unaffected regardless of concentration or frequency of treatment with ethene.
Other studies found that if exposure to ethene was terminated prior to irreversible effects, such as leaves falling off, plants were capable of recovering from exposure Klassen and Bugbee Given these kinds of emission data, it is very unlikely that plants are being exposed to ethene for sufficiently continuous lengths of time to cause long term impacts.
While individual release events may cause very high concentrations of ethene in the atmosphere for a short period of time, these exposures are limited in time due to the rapid dispersal of ethene in the environment and the lack of long-term or prolonged exposure. Short-term exposure exceeds the PNEC approximately once per year and the long-term exposure values reflect the highest annual concentration in all years, including concentrations occurring over the winter months.
Some species of plants exposed to high concentrations of ethene can show an increase in epinasty, root length reduction, flower abscission, and ripening of the flower or fruit. However, these concentrations have also been found to promote fruit ripening and increase seed yield. Additionally, plants exposed in the environment tend to show a greater resistance to ethene exposure compared to plants studied in laboratory settings and, in both cases, when plants are given a recovery period, recovery can often be seen, especially in regards to leaf curling and growth inhibition.
Ethene is a naturally occurring substance and it is produced and used in large quantities in Canada. Anthropogenic releases are expected to be exclusively to air, mainly from combustion of fossil fuels vehicle emissions and industrial processes. Ethene is not persistent in air and has low potential for long range transport.
It is also not bioaccumulative. Ethene is a precursor to ground level ozone. As well, a common degradation product of ethene in air is formaldehyde. Terrestrial plants are highly sensitive to ethene in air. However, risk quotients showed ambient concentrations were unlikely to have impacts in urban areas or in rural areas over either short- or long-term exposures. A risk quotient analysis using industrial ethene monitoring data for the years — indicated that there is, on average, one occurrence per year that has the potential to be harmful to terrestrial plants due to industrial emissions of ethene.
A risk quotient analysis was not performed for terrestrial mammals as mammalian toxicity values were orders of magnitude greater than air concentrations expected to occur in Canada. A major anthropogenic source of ethene is the internal combustion engine, which explains in part why ethene air concentrations in Canadian cities can be considerably higher than in rural and remote areas.
Advances have been made in the last 20 years in reducing pollutants, including ethene, from the exhaust of internal combustion engines. There appears to be a trend to lower air concentrations in Canadian cities, even over the last 10 years, which follows the reductions in other pollutants from automobile exhaust.
Further reductions are expected as a result of more stringent requirements for NOx, SOx, and VOCs in automobile exhaust and with continual removal of older cars from use. Facilities manufacturing, processing, or otherwise using more than 10 tonnes per year of the substance must report their releases to the National Pollutant Release Inventory NPRI. In , facilities across Canada reported to the NPRI on-site environmental releases totalling approximately tonnes.
Based on the information presented above, there is low risk of harm to organisms or the broader integrity of the environment from this substance. It is therefore concluded that ethene does not meet any of the criteria under paragraphs 64 a or b of CEPA, as it is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.
The responses of specific plants to ethene are difficult to predict, as even closely related species can have variable responses when tested simultaneously. The duration and concentration of exposure to ethene are both important variables when considering the effects of ethene on plants, however, many studies only addressed one of these variables at a time. Additionally, there are few tests that specifically address sensitive life stages of plants as most studies focus on horticultural concerns such as flower appearance for the purpose of the transportation of cut flowers.
The most sensitive species available in addition to the most sensitive cultivar of that species was used to maintain a conservative approach to determining potential impacts on plants. The endpoint chosen for short-term exposure represented a significant effect and it is possible that lower concentrations may have still had a significant effect on barley.
The long-term exposure scenario for ethene assumed that the modelled value of 5. It is likely, based on monitoring data, that background concentrations are lower than those supposed in the Archambault and Li study. Ecotoxicity ground surface soil In general, contamination of soil by corn farming contributes to this impact category.
Extensive use of chemical fertilizers and pesticides for corn production results in the contamination of soil by metals such as zinc, copper and nickel which constitute approximately 0. In , the consumptions of nitrogen-, phosphate- and potash-based fertilizer were 4. Common agricultural practices such as conventional tilling practice of turning or digging up soils to prepare fields for seeding new corn remove organic residue from the top soil surface left by previous harvests or cover crops, further exacerbating the fertilizer requirement for cultivation.
In comparison, soil pollution is negligible for ethylene production from crude oil and natural gas. Ecotoxicity — Water In general, partitioning of metals copper, nickel and chromium and non-metals arsenic into water reservoirs, lakes, and rivers contributes to this impact category.
Leaching of the heavily fertilized top soil during corn farming by run-off of rain water or from irrigation is a major reason for this contamination. Inadequate rain and extensive irrigation during cultivation also adversely impact the local ecosystem due to the exhaustion of the water table and reduced water levels in water reservoirs, lakes and rivers.
Water is also used in the fermentation of corn to ethanol 1. For comparison, 2—2. Eutrophication Erosion of fertilized soil containing ammonia, nitrates and phosphates in corn farming and N 2 O emissions are the main causative factors in eutrophication of fresh water [ 46 ].
The direct emission caused by the microbial and chemical reduction of nitrates biological denitrification and chemodenitrification , addition of mineral N-containing substrates ammonium phosphate , animal manures, crop residues, nitrogen-fixing crops and sewage sludge to agricultural soils are the major sources of N 2 O emissions [ 49 , 50 ]. Approximately, 1. In comparison, the eutrophication potential for naphtha from crude oil is substantially lower 0.
The overall environmental impact of ethylene production is thus similar for naphtha, ethane, and corn-ethanol feedstocks. It should be emphasized that ethylene sourced from cellulosic ethanol will have a different environmental impact. In the following section, an analysis is performed to quantify and compare the environmental impact of producing energy from other fossil fuel sources coal and fuel oil as well.
The foregoing LCA of ethylene production from various feedstocks assumes natural gas as the source of process energy. To determine the effect of the energy source, we also performed environmental impact assessments to quantify the impacts of generating process energy from various fossil fuels such as coal hard coal, lignite , fuel oil heavy fuel oil, light fuel oil and natural gas.
In each case, the cumulative environmental impacts of burning the fuels to produce 1, MJ of energy consider a extraction of the fuel from its source; b transportation of the extracted fuel to the power plant; and c production of 1, MJ energy at the power plant. Coal is classified based on carbon, ash and inherent moisture content. Hard coal, also known as anthracite, is the best quality coal with a high carbon content and calorific value. Lignite, commonly known as brown coal, has a relatively lower energy content due to high inherent moisture and ash contents [ 51 ].
In the USA, lignite coal is primarily used for electricity production whereas hard coal is used for metal processing. The difference in these impacts is attributed to the emissions from a power generation facility. As shown in Table 3 , the predicted impacts for coal from an underground mine are greater than those for a surface mine in most categories except water pollution. However, the differences lie within the prediction uncertainty. Further, the Greenhouse Gas GHG emissions global warming potential from burning at the power plant [ This facility utilizes anthracite coal obtained from a surface mine [ 53 , 54 ].
Table 4 lists the environmental impacts of extracting and transporting natural gas from reservoirs, and of producing 1, MJ energy from natural gas at a power plant. Heavy fuel oil Number 6, residual fuel oil, bunker fuel oil mainly comprises residues from cracking and distillation units in the refinery. Table 5 compares the predicted impacts associated with fuel oil production high boiling fraction of crude oil and emissions associated with the burning of both heavy and light fuel oils.
The impacts of generating energy from heavy and light fuel oils are similar, with the differences being within prediction uncertainty. The major sources of pollution are discussed in the following section. This is primarily attributed to the low carbon content and the higher calorific value of natural gas. This analysis however assumes that there is no contribution to GHG emissions by natural gas leakage.
Acidification potential of the various energy sources is dictated by the sulfur content and the associated SO 2 emissions during fuel burning. While NO X emissions result from fuel burning, the actual amounts are relatively small. This is because of the fact that energy production from lignite requires state-of-the-art SO X and NO X abatement technologies to meet the stringent environmental regulations. The higher S content in heavy fuel oil results in higher acidification potential compared to light fuel oil Table 5.
Ecotoxicity — air The metal emissions for coal and heavy fuel oil are greater than light fuel oil and natural gas by an order of magnitude Tables 3 , 4 , 5. In coal, zinc is present in the sphalerite form that has a low melting point and hence is easily susceptible to vaporization resulting in metal emissions. Heavy metal emissions such as chromium in fuels depend on the properties and concentration of metals and the technologies used for combustion and post-combustion cleanup.
Human health cancer air Potential metal emissions for energy production from hard coal, lignite and heavy fuel oil are similar but an order of magnitude greater than those reported for natural gas and light fuel oil Tables 3 , 4 , 5.
Combustion of coal anthracite and lignite produces significant arsenic emissions, which have high toxicity and persistence [ 58 ].
Potential metal emissions for energy production from hard coal, lignite and heavy fuel oil are similar but an order of magnitude higher than that reported for natural gas and light fuel oil Tables 3 , 4 , 5. Combustion of coal also produces mercury, nickel and chromium emissions [ 58 ]. In , mercury emissions from coal-fired plants using state of the art mercury capture techniques are approximately 0.
The mobility of arsenic in the atmosphere during mining, combustion and storage of coal is dependent on its mode of occurrence. Arsenic in hard coal and lignite is present in the pyrite organic phase. The storage facilities and waste material are major sources of arsenic mobilization. Clean coal technologies, employed to reduce sulfur content, are known to reduce arsenic concentration resulting in lower arsenic emissions during energy production from lignite [ 61 ]. The results from the foregoing analysis can be easily scaled to reflect per capita environmental impacts and can therefore be utilized to quantify the environmental impacts of energy production from various energy sources in general.
For ethylene production from naphtha, the composition of the crude oil has a significant influence on the overall environmental impact. For example, increased sulfur and nitrogen contents in crude oil will adversely impact the process energy requirement and overall yield of the process. In the case of ethylene from ethane cracking, the inclusion of fugitive emissions during the handling of natural gas, such as methane with a global warming potential of 25 times that of CO 2 on a weight basis , will significantly worsen the overall environmental impact.
For ethylene from corn ethanol, the environmental impacts can be lower under the following scenarios: increased ethanol yields either due to the development of genetically modified corn or commercialization of technologies that can process both corn and corn stover cellulose, hemi-cellulose and lignocellulose ; and development of corn strains that require less fertilizer and water and also have a higher resistance to pests. The rate of CH 4 and C 2 H 4 production in the control treatments i.
The highest production rates for both gases were measured for LDPE. Most of the samples kept in the dark did not produce any gas, and those that did had much lower production rates, reaching pmol CH 4 g -1 d -1 and 60 pmol C 2 H 4 g -1 d -1 for PS, and 50 pmol CH 4 g -1 d -1 and 20 pmol C 2 H 4 g -1 d -1 for PET and AC, respectively.
The spectra derived from Raman analysis on plastic debris pieces collected from the open ocean were compared with different types of commercially sourced common plastics. For both types of plastic, the cumulative amount of hydrocarbon gases increased with time although the relative contribution of the gases produced was variable Fig 1A and 1B.
The rates of hydrocarbon gas production are normalized to weight and to convert to surface area, the pellet weight of approximately 35 mg had a surface area ranging from ca.
Gas production rates increased over time for the virgin pellets Fig 1C but were relatively constant for the aged plastic Fig 1D. Except for CH 4 , the weight-normalized gas production rates were lower for the aged plastic compared to virgin pellets. Measurements were taken at approximately two-week intervals during the incubation period. Error bars represent the error propagation of the standard deviation of the mean for each time point.
CH 4 and C 2 H 4 production rates from virgin LDPE pellets were larger for similar incubation periods when the plastic was exposed to sunlight directly in air Fig 2 , rather than immersed in water Fig 1. In that case, production rates for both gases increased with time and ranged from 0. No detectable emissions of any of the gases were observed in the control or dark treatments data not shown.
The error bars represent the standard deviation of triplicate samples. The emission of CH 4 in the dark treatment was below the detection limit and less than 0. All dark treatments showed emission rates less than 0. Error bars represent the standard deviation of triplicate samples. LDPE pellets incubated in the dark after exposure to light produced measurable quantities of hydrocarbon gases. The rates of CH 4 0. In addition, environmentally-aged LDPE plastic collected from the open ocean and incubated for 14 days in the dark under ambient outdoor temperature [ These results indicate that once initiated, the production of hydrocarbon gases continues in the dark.
Morphology has an important effect on hydrocarbon gas production. No other consistent pattern for the other hydrocarbon gases was observed with the different densities. Interestingly, the ratios of the different gases produced varied across LDPE pellet densities. For example, the C 2 H 4 : CH 4 ratio varied from 1. Our results show that different types of plastics, that are commonly used and dispersed in the environment worldwide, produce CH 4 and C 2 H 4 under environmental conditions.
We hypothesize that the relative amounts of low-molecular-weight hydrocarbon gas molecules that are released from plastic substrates depend on the molecular structure of the plastic including the degree of branching, the addition of plasticizers, as well as the manufacturing process. For example, among the plastic materials tested, LDPE produced the largest amounts of CH 4 and C 2 H 4 , probably due to its weaker structure and more exposed hydrocarbon branches. In contrast, with a more compact structure, lower permeability and fewer accessible active sites, degradation of HDPE resulted in lower emission.
The release of greenhouse gases from virgin and aged plastic over time indicates that polymers continue to emit gases to the environment for an undetermined period. We attribute the increased emission of hydrocarbon gases with time from the virgin pellets to photo-degradation of the plastic, as well as the formation of a surface layer marked with fractures, micro-cracks and pits [ 24 — 26 ].
With time, these defects increase the surface area available for further photo-chemical degradation and therefore might contribute to an acceleration of the rate of gas production. The initial shape of the polymer is also a potential factor contributing to the variability in hydrocarbon production because items of the same mass but with different shapes have different surface-to-volume ratios.
Small fragments not only have a greater surface-to-volume ratio than larger items, but they also tend to have longer edge lengths relative to their volume [ 29 ]. This predicts that in the environment, as plastic particles degrade and become smaller, they will also emit more hydrocarbon gases per unit mass. The emission of gases from the aged plastic collected from the ocean age unknown at the start of the experiment indicates that production may continue throughout the entire lifetime of the plastic.
We hypothesize that lower production rates from environmentally aged plastic are probably due to the presence of plasticizers that retard photo-degradation by counteracting the negative effect of UV radiation. Manipulation of the radiation spectrum showed that UVB increases the production of hydrocarbon gases relative to longer wavelengths, which is consistent with its key role in the photo-oxidative degradation processes for polyethylene [ 26 ].
Indeed, solar photon flux, especially in the UV portion of the spectrum, provides the activation energy necessary to initiate degradation due to bond cleavage and depolymerisation, which affects the mechanical properties of the material [ 26 , 30 , 31 ].
We hypothesize that this process yields hydrocarbon gas molecules that are released into the environment. Although the emission of hydrocarbon gases is enhanced by photo-degradation in the UVB spectrum, our results indicate that UVB radiation is not essential for the initiation or the continuous production of hydrocarbon with time. Once initiated by solar radiation, emission of the gases continues in the dark, at a rate that depends on previous radiation exposure. While the production of hydrocarbon gases was prevalent in LDPE, the different morphologies and densities within LDPE products resulted in a change in the relative concentrations of the different gases.
LDPE in powder form, with a much higher surface area than pellets with the same density and weight, produced the highest amount of hydrocarbon gases.
Along with morphology and density, the average molecular weight that varies with the polymer chain length and hence the number of branched molecules exposed may also be a controlling factor in hydrocarbon emissions. Unfortunately, this information is proprietary and very rarely available from suppliers. Also, even polyethylene, which is known to be the simplest polyolefin, can form various conformational structures of the macromolecular chains, which in its solid state assume various states of intermolecular order [ 10 ].
This heterogeneity within the same type of plastic would affect the production rates of the different hydrocarbon gases and consequently the ratios among them. Yet, due to the heterogeneity of the products even within the same type of plastic, the nature of the reactions is unknown. The shortening of the long polymer chain and its breakdown into smaller units can be caused by different mechanisms such as random chain scission, end-chain scission, chain-stripping or cross-linking [ 28 ].
These reactions would lead to the production of hydrocarbon gases including those presented in this study. The global production of plastic is large [ 1 ] and the amount of plastic waste generated in from countries was x10 6 Mt from which 4.
By , the amount of plastic waste input to marine systems might increase by an order of magnitude if waste management is not improved [ 32 ]. Because polyethylene is the most common polymer, it is anticipated to be the most common form of plastic pollution in surface ocean waters worldwide [ 33 — 35 ]. In addition, as microplastics with greater surface area are produced hydrocarbon gas production rates will likely accelerate.
The results from this study indicate that hydrocarbon gas production may continue indefinitely throughout the lifetime of plastics. The amount of plastic material in the environment exposed to full sunlight exceeds the quantity of submerged plastic.
Our experiments indicated that emissions of hydrocarbon gases are even greater up to 2 times higher for CH 4 and up to 76 times higher for C 2 H 4 in air compared to in water.
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