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Multivariate Analysis of Heavy Metal Contamination in Urban Dusts of Xi'an, Central China
Abstract and Figures
Though there are many studies of heavy metal contaminations of urban dusts in developed countries, little attention has been paid to this kind of study in developing countries, including China. Therefore, a series of investigations were performed to provide heavy metal signatures of urban dusts and to evaluate potential sources in Xi'an, Shaanxi Province. Sixty-five samples of urban dusts were collected in Xi'an. Then Ag, Cr, Cu, Mn, Pb and Zn concentrations were determined by using atomic absorption spectrophotometry, and As, Hg and Sb concentrations by atomic fluorescence spectroscopy. The results indicate that, in comparison with Chinese soil, urban dusts in Xi'an have elevated metal concentrations as a whole, except those of arsenic and manganese. These concentration levels are comparable to those in other studies. Correlation coefficient analysis, principal component analysis (PCA) and cluster analysis (CA) were performed and three main sources with corresponding cluster elements were identified: (1) Ag and Hg have commercial and domestic sources; (2) Cr, Cu, Pb, Sb and Zn are mainly derived from industrial sources, combined with traffic sources as well for Pb and Zn; (3) As and Mn come mainly from soil sources, and As also has an industrial source. Based on PCA and CA analyses, manganese was selected as the reference element, and heavy metal enrichment factors (Efs) were calculated, which in turn further confirms the source identification. Also, Efs give an insight of human influence degree of urban dusts.
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... The Enrichment Factor (EF) is defined by Yongming et al. (2006) as Eq. (2): where X represents the element of interest and Ref the reference element respectively in the sample (numerator) and in the calculated regional baseline (denominator). ...
... In this study, we used aluminum as a reference element based on these considerations: (1) it is high natural abundance, (2) it is considered as a conservative element undergoing minimal disturbance by biological, diagenetic, and redox processes (Rollinson, 2014), and (3) it is easily determined by conventional techniques. The categories based on Enrichment Factor (EF) were (Yongming et al., 2006): EF < 2 Deficiency to minimal enrichment; 2 < EF < 5 Moderate enrichment; 5 < EF < 20 Significant enrichment; 20 < EF < 40 Very high enrichment; EF > 40 Extremely high enrichment. ...
... All indices were calculated for all samples using the regional geochemical base values (RGB) as a reference value. Previous studies (Sappa et al., 2020;Sierra et al., 2015;Yongming et al., 2006) have highlighted the need to use the local baseline values to define the soil contamination status. Figure 3 illustrates the values of the indices calculated for the elements of toxicological and technological interest. An analysis of the individual indices reveals that the EF for all the elements considered is consistently below 2, which, according to the classification by Yongming et al. (2006), indicates a status categorized as "Deficiency with minimum enrichment"; the CF values range between 0 and 1 for all elements, corresponding to a "Low contamination factor" in according to the classification of Rutkowski et al. (2020). ...
This study presents a comprehensive investigation of the geochemical baseline values and the spatial distribution of major, trace elements, and rare earth elements in the unpolluted soils of Sicily region. The concentrations of elements were quantified by ICP-OES and ICP-MS. The distribution patterns of major and trace elements are closely linked to the geological features of the area. The major elements Fe, Ca, Al, Mg, and K exhibit the highest concentrations. The order of abundance for trace elements follows this trend: Ba, Sr, Zn, V, Cr, Cu, Rb, Ni, Pb, B, Li, Co, As, Mo, U, Sb, Se, Cd, and Bi. Regional geochemical baseline values were calculated using the UTL95 - 95 method with BCA bootstrap, demonstrating that the regional approach provides a more accurate assessment compared to European and Italian threshold values. A geostatistical approach was used to produce spatial geochemical maps, which allow the prediction of element distributions in unsampled areas. This integrated approach establishes a benchmark for more detailed studies on environmental risk assessment, providing a solid foundation for identifying and understanding natural and anthropogenic geochemical anomalies in the soils of the Sicily region.
... There was a correlation between the different elements, as shown in Table 3, where the correlation coefficients between Ni and V, Zn, Co, Cr, and Mn were all greater than 0.9. The greater the correlation, the more similar the geochemical behaviour of the different elements (Han et al., 2006). Analysing the complex sedimentary process and reconstructing the sequence of environmental changes Medium Subcircular-Subangular through the changing trend of each elementis tedious, and may also lead to contradictory conclusions (Chen et al., 1999). ...
The Late Mesozoic is a typical period for studying the greenhouse climate and the interaction of the Eearth’s systems. To expound the interaction between the evolution process of the terrestrial surface system and the environment in the Late Jurassic -Cretaceous, a typical profile with relatively complete exposure of the Mesozoic strata in the Emei area of the Sichuan Basin, the Chuanzu Profile, was selected for this study. The sedimentary environment of the study area was qualitatively analysed based on the macroscopic characteristics of the lithostratigraphy of outcrop profiles in the field and the statistical data of detrital composition under a microscope. Factor analysis and the chemical alteration index after correction (CIAcorr) were used to quantitatively analyse the characteristics of major and trace elements. Finally, the palaeoclimatic evolutionary characteristics of the Late Jurassic-Cretaceous in the Emei area are systematically discussed. The results show that the formation of Cretaceous sediments in the Emei area of the Sichuan Basin is mainly controlled by climatic factors, but is little affected by tectonic activities, and the maturity of the rock clastic composition is relatively low; therefore, it should be a near-provenance deposit. The range of CIAcorr values was 55–79, indicating that the degree of chemical weathering of the provenance was weak to moderate. The palaeoclimate in the Late Jurassic gradually became humid from Early to Late; in the Early Cretaceous, it was semiarid to semihumid, with an extremely dry event occurring; and in the Late Cretaceous, it was semiarid and drier than that of the Early Cretaceous.
... Moreover, the significant impact of other nocturnal destruction processes such as absorption and ground deposition cannot be excluded, even though they do not affect O 3 and NOx in the same way (Toh et al. 2013 "PCA", hierarchical cluster analysis (HCA) and multiple linear regression analysis "MLRA". PCA and HCA have been used to investigate air pollution data with respect to source identification and characterization (Han et al. 2006;Tokalioglu and Kartal 2006;Liu et al. 2014). MLRA has been used as a statistical model to examine the relationship between dependent and independent variables (Bai et al. 2018). ...
This study examined the temporal variability of PM10, surface ozone (O3), NOx (NO + NO2) and CO in Kairouan (Central Tunisia), during May 2013 which was characterized by its very particular meteorology. The results showed that maximum daily concentrations of 467 µg/m³, 34 ppb and 39 ppb were recorded for PM10, surface O3 and NOx, respectively. The CO daily concentrations appeared almost constant, around 1.2 ppm. The PM10 individualized peaks occurring during May 1st–4th, 18th and 21st–22nd were attributed to the effect of severe Saharan dust storms associated with an intense subtropical cyclone threatening the most European regions. The recorded O3 concentrations and their nitrogen and carbon precursors were shown comparable, respectively, during and outside dust storm events. The O3 accumulation rate was approximately equal to 2 ppb/h. The rate coefficient (k3) for the NO-O3 reaction, and the NO2 photolysis rate j1, at 16:00 LTh, were found to be 17 ppm⁻¹ min⁻¹ and 0.25 min⁻¹, respectively. Such values were slightly lower than that found in other Tunisian regions. PCA and HCA statistical approaches highlighted the O3 production processes through NO2 photolysis and CO oxidation, as well as its destruction due to NO titration and absorption. Multiple linear regression analysis revealed that wind speed and NO have the greatest influence on O3 concentrations variability. Air Quality Indices showed elevated values only during dust storm events, with PM10 contributing to AQI levels as high as 125, signaling poor air quality and heightened health risks during these episodes.
... The results demonstrated a significant increase in Fe, Cu, Cr, Ni, As, and Co in X. parietina and F. hygrometrica from the third to the first site ( Figures 5 and 6). The elevated Fe and Cr concentrations near the first site may be attributed to emissions from the nearby petrochemical industrial complex (Figure 1) [68,69] and road traffic, given that daily vehicular movement on the Bizerte-Tunis Highway contributes to contamination [70]. Cu, a well-known tracer for gasoline emissions [71], was also found in high concentrations near the first site. ...
Atmospheric emissions of industrial-origin trace metals are a major environmental problem that negatively affects air quality and the functioning of forest ecosystems. Traditional air quality monitoring methods require investments in equipment and infrastructure. Indeed, it is difficult to measure most of these pollutants because their concentrations usually occur at very low levels. However, this study explores an ecological approach for low-cost air quality biomonitoring that is based on native biological indicators in the context of the Mediterranean basin. This study aims (i) to evaluate the lichen species composition, diversity, and distribution across three distinct forest sites; (ii) investigate the relationship between lichen species richness and proximity to the pollution source; and (iii) evaluate heavy metal bioaccumulation using a moss species (Funaria hygrometrica) and a lichen species (Xanthoria parietina) as bioindicators of atmospheric pollution. High concentrations of toxic metals were observed along the transect and closer to the pollutant source with marked interspecies variability. X. parietina exhibited high bioaccumulation potential for most toxic metals (Fe, Zn, Pb, Cr, Cu, and Ni) compared to F. hygrometrica with concentrations varying across the three sites, reaching maximum dry-mass values of 6289 µg/g for Fe at the first site and 226 µg/g for Zn at Site 3. Our results suggest that X. parietina can be used as a potential bioindicator for long-term spatial biomonitoring of air quality by determining atmospheric toxic metals concentrations.
... These geochemical indices and toxicity measurements were developed to evaluate contamination levels and ecological risks in aquatic environments including both estuarine and freshwater systems (Zhang et al., 2016;Huang et al., 2019;Proshad et al., 2022;Ustaoğlu & Tepe, 2019). On the other hand, to identify potential sources contributing to these toxic substances, multivariate chemometric techniques such as correlation and principal component analysis (PCA) can be utilized Micó et al., 2006;Yongming et al., 2006). ...
Heavy metal contamination in estuarine environments poses substantial risks to ecological integrity and human health. Notably, El Salvador is experiencing one of the worst water crises in Central America, with more than half of its water bodies polluted. This study focuses on sediment chemistry contributions to macroinvertebrate declines in La Barra de Santiago Estuary following the 2005 eruption of the Santa Ana volcano and potential interactions with anthropogenic contributions to the ecosystem. Various contaminants were measured to determine the sediment and water quality. Geoaccumulation index, combined pollution index toxic risk index, and pollution load index were evaluated in bottom sediment and indicated significant contamination, particularly driven by elevated Ni concentrations. The sources of these metals' inputs are not clear from analysis of pairwise associations. Principal component analysis was used to evaluate source contributions by comparing the chemical compositions of potential sources, such as fertilizers, volcanic ash, and other agrochemical source chemistries with the sediment chemistry in component space. This approach helped identify patterns and relationships between the sources and sediment contamination. These findings not only clarify Central American estuarine sediment chemistries but also reveals surprising Ni contamination in these sediments.
... Os valores médios de todos os FEs foram classificados no máximo em moderado, sugerindo que a maior parte dos sedimentos amostrados são provenientes de fontes naturais (Yongming et al., 2006). De forma semelhante temos o Fator de Contaminação (FC), que apresentou também a maior parte das amostras sendo classificadas como contaminação moderada e baixos percentuais enquadrados como contaminação considerável a elevada. ...
The Jequitinhonha river basin stands out for its heterogeneity.
The objective of this research is to present an environmental
assessment of the quality of sediments and the availability of surface waters through environmental indices for a portion of the basin located in the Northeast of the State of Minas Gerais. Using data from monitoring stations, historical series of rainfall, river flows and suspended sediments from 1990 to 2021 and evaluating land use and occupation data from the years 2000, 2007 and 2011. Obtaining concentrations of EPTs by ICP-OES and ICP-MS. The calculation of environmental indices demonstrated that the highest concentrations occur in areas where lithologies are naturally rich in EPTs. However, temporal data showed that since 2007, the Middle-Lower Jequitinhonha started to suffer reductions
in river flow and suspended sediment load caused by the installation of the Irapé Hydroelectric Plant.
... Interestingly, only As had high variability in bare soils, lateritic plateaus, and vegetable gardens (104,147, and 157 %), suggesting that, in addition to mining, other land uses might have partially contributed to As distribution (Table 1). It can be inferred that artisanal gold mining and farming were by far the most anthropogenic activities that affect PTE loadings in the soils [79][80][81]. ...
... PCA is one of the important statistical techniques introduced by Pearson (1901) and improved by Hotelling (1933). It is a data reduction tool (Loska and Wiechula 2003) used for the conversion of huge numeral of analyzed variables/parameters into small numeral of factors required for the analysis of interrelationship among the analyzed parameters (Yongming et al. 2006). The summary of PCA along with eigenvalues, total variance and communalities are given in Table 4 and 5. ...
Hydrogeochemistry of meltwater along with chemical weathering and suspended sediment transport in the glacial environment plays an important role in the assessment of meltwater quality, dissolved load, chemical weathering rate, consumption of CO2 from the atmosphere and suspended sediment flux in the glacierized area. HCO3− was the abundant anion in the Gaglu glacier meltwater constituting 67.6%, 74.9%, 77.6% and 74.6% of TZ− (total anions) during the study period 2015, 2017, 2018 and 2019, respectively. While, Ca2+ was the dominant cation constituting 54.2% in 2015, 55% in 2017, 57.5% in 2018 and 56.8% in 2019 of TZ+ (total cations) in the glacial stream meltwater. High equivalent (Ca + Mg) versus TZ+ and (Ca + Mg) versus (Na + K) ratios and low (Na + K) versus TZ+ ratio in the meltwater for all the four years of study shows that carbonate weathering regulates stream water hydrochemistry of the Gaglu glacier followed by silicate weathering. The mean dissolved load of the Gaglu glacier was estimated to be 25.5 t/day. Carbonate weathering rate (CWR) (78.7 t/km2/year) in the Gaglu glacier basin shows higher value with respect to silicate weathering rate (SWR) (27.4 t/km2/year). Total CO2 consumption rate [φCO2] via chemical weathering (contains both carbonate and silicate weathering) in the glacier basin has been calculated to be 17.6 × 105 mol/km2/year during the observation period July 2019. The annual CO2 drawdown by the Gaglu glacier basin (843 × 105 mol/year) is higher in comparison to the Batal glacier basin situated in the same region (i.e. Chandra basin), which might be due to high glacial stream discharge and bigger size of the Gaglu glacier as compared to the Batal glacier. The average value of suspended sediment load (SSL) and physical weathering rate of Gaglu glacier was calculated to be 841 t/day and 6402 t/km2/year, respectively, which shows higher value with respect to the Chhota Shigri glacier situated near the Gaglu glacier.
... The significant variation in heavy metal content across dust samples highlights the heterogeneous distribution of these contaminants in various study areas. This heterogeneity is influenced by a complex interplay of factors, including local pollution sources [42,43], meteorological conditions [44,45], and topographical features [46]. Urban runoff, particularly from highways, is a significant source of lead, copper, cadmium, and zinc. ...
Rapid urbanization and associated transportation play a crucial role in the distribution of heavy metals in road dust, leading to serious environmental and health concerns. This study explored the concentration and spatial variability of metals, including cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn), in road dust across six urban zones in Guangdong Province (parks, educational, residential, commercial, traffic, and industrial areas). The study also evaluated the bioavailability of these metals to determine their carcinogenic and non-carcinogenic health impacts. The findings revealed significant variations in metal levels, with commercial zones having the highest concentrations of Zn 1316.1 ± 381.6 mg/kg), Cu (426.1 ± 136.7 mg/kg), and Cd (1.29 ± 0.08 mg/kg) due to the deposition of traffic emissions. The bioaccessibility of Pb, Zn, and Cd was found to be higher in the gastric phase, suggesting increased absorption potential when ingested. Children were at a significantly higher non-carcinogenic risk compared to adults, facing more than double the exposure. While the carcinogenic risk from Pb was low but notable, Cd presented minimal risk. These results highlight the need for targeted interventions, including stricter emission regulations and public health strategies, to mitigate the risks of heavy metal exposure in urban areas.
Phosphorite exploitation poses environmental risks due to potentially hazardous elements (PHEs). This study investigates their distribution, fractionation, and origin in Algeria’s sedimentary deposits. Whole-rock (n = 16), grain size fractions (n = 15), and phosphate particles (n = 32) were analyzed using petrographic, SEM-EDS, ICP-MS, and LA-ICP-MS techniques. Robust Principal Component Analysis (Robust PCA) and environmental indices, including enrichment factors (EF) and potential ecological risk index (PERI), were applied. Samples contains carbonate-fluorapatite (CFA) with minor carbonate and silica, while SEM-EDS occasionally detects sulfide inclusions in P-particle pores. Chemical analysis reveals high CaO and P2O5 (up to 45 and 38 wt%, respectively), along with elevated Sr (516–2597 mg/kg), Zn (106–609 mg/kg), Cr (199–348 mg/kg), Cd (0.5–143 mg/kg), and U (11–126 mg/kg). According to Robust PCA, CFA hosts, through substitutions, U, Sr, Y, V, Cr, Pb, Cd, Cu, and Zn, while the matrix retains Nb, Rb, Ta, Hf, Zr, Li, Cs, Mo, As, and Th, via adsorption. Fine fractions and glauconite show enhanced PHEs, with peak enrichment at the Paleocene-Eocene transition. Environmental assessments reveal extreme ecological risks, particularly from Cd and U, necessitating selective mining to mitigate contamination in PHE-enriched layers, along with appropriate waste management.
Cascade impactor and bulk samples of atmospheric aerosol particles were collected at three sites on the Tibetan Plateau: Udaoliang (September 1993 to May 1994) and Lhasa and Gongga (May 1998). The average dust concentration at these ground-based sites was 82mugm-3 this is lower than the lowest average concentration observed over the nine major Chinese deserts (arithmetic mean value of 270mugm-3), and it also is lower than that over the Loess Plateau (170mugm-3). The elemental mass-particle size distributions for several major dust-derived elements (Al, Ca, Fe, K, Mn, Si, and Ti) were approximately lognormal, but those for Al, Fe, and Ti differed from Ca, K, and Si. Dry deposition velocities calculated from the observed size distributions and a two-layer deposition model averaged 2.7cm-1 for Al, Fe, and Ti. For Ca, K, and Si, which appear to be more strongly affected by local Tibetan sources, the average calculated dry deposition velocity was 4.3cms-1. Wet deposition fluxes estimated from scavenging ratios indicate that less than 10% of the total deposition on the Tibetan Plateau is attributable to wet removal during the 9 months for which data are available. The yearly mean dust deposition rate (local plus remote and dry plus wet) is estimated to be of the order of ~100gm-2yr-1, which is lower than that onto the Chinese desert regions (320gm-2yr-1) or the Loess Plateau (250gm-2yr-1), suggesting that the sources upwind of China, and the Tibetan Plateau itself, are not major sources for Asian dust.
Trace and major elements were measured in sediment cores collected at the shelf and continental slope of the Banc d’Arguin (Mauritania). Most of the sediments have a calcium carbonate content >50% and as a consequence have a low aluminium (<1.5%) and iron (<1.0%) content. The concentrations of the latter two elements increase down slope. Based on the major elemental composition, the sediments seem to be well mixed and concentration gradients are only observed on a spatial distribution. Concentrations of Cu, Cd, Zn, Ni and Pb are low and approximately equal to “natural background” values, indicating negligible anthropogenic influences. An exception is Cd for which very high values were found in the northern most part of the research area, close to Nouadhibou. A possible explanation for this high Cd content can be the existence of phosphate rich sediments with a high affinity for Cd. Small increases in the available trace metal concentrations (exchangeable fraction, 0.1 N HCl treated) observed near the sediment surface could be attributed to early diagenetic processes, and not to pollution effects. The inputs from the Saharan dust plume with low trace metal contents, the transport of small particles with higher trace metal content down slope together with the escape of redissolved trace metals from the sediment, and the absence of a supply of metal rich material to the Banc d’Arguin, has created a metal poor environment. There is clear evidence of trace metal redistributions, associated with Mn recycling. Mean enrichment factors, calculated relative to the crustal abundance, show that Zn, Pb and Cd are equal to unity and Cu and Ni below unity. These observations suggest that the Cu and Ni contents in sediments of Banc d’Arguin are depleted relative to the accepted values in the earth crust. The very low trace metal concentrations detected in these sediments can be taken as “baseline” values for unpolluted sediments in the global ocean coastal zone.
Concentrations of several trace elements have been measured in air samples collected simultaneously at four remote stations from SW Sweden, along the Norwegian coast to north Finland. The samples showed that the background aerosol had a large spatial variation in elemental composition. During cases of long-range transported air pollution (episodes), concentrations of pollutants were several times higher than the background concentrations. Generally, the background concentration profile varied, showing a decrease in concentrations towards northwest. The levels of some elements were elevated at the northernmost station as a result of influence from the industrialised areas at the Kola Peninsula. Trends of concentrations from 1985 and onwards were followed at one of the sites. The highest concentration of trace elements in the fine fraction of particles was observed in the mid-1980s, and a considerable decrease is observed during later years. Elemental signatures were calculated and compared with the same ratios from large source areas.
Estimates of atmospheric dust deposition to five Asian/Pacific regions indicate that -800 Tg of Chinese desert dust is injected into the atmosphere annually; about 30% of this is redeposited onto the deserts, 20% is transported over regional scales, primarily within continental China. The remaining 50% of the dust is subject to long-range transport to the Pacific Ocean and beyond. Elemental tracers based on several dust- derived elements (A1, Fe, Mg, and Sc) reveal high-frequency variability in the contributions of the western desert sources versus northern high-dust and low-dust desert sources to eolian deposits from the center of the Loess Plateau. Comparisons of the patterns uncovered with climate signals from the remote North Atlantic region for the last glaciation show that shifts in source areas of Asian dust were synchronous with large-scale variations in atmospheric circulation.
Several techniques for the analysis of lead in street dust have been reported in the literature. The results presented here are an attempt to determine the influence of analytical technique on the reported lead levels. The results indicate that mean lead level is depressed by sample grinding, and by increases in ashing temperature. Higher lead levels are produced by refluxing in comparison with simple boiling. When four techniques were evaluated separately differences of between 250 and 450 mg kg−1 were found, which could be ascribed solely to differences in technique.
A rugged, sensitive, semi-automated method for the determination of trace-level mercury in small rat brain tissue samples by cold vapor atomic fluorescence spectrometry (CVAFS) is described. Small tissue aliquots (100 mg) are digested for 6–8 h at an elevated temperature in a mixture of nitric and sulfuric acids. Following digestion, samples are oxidized with potassium bromate/bromide at room temperature and treated with a continuous flow of stannous chloride to generate mercury vapor. The experimentally determined method quantitation limit (MQL) in the rat brain matrix is 10 pg Hg/mL, which corresponds to 1.5 ng Hg/g brain tissue. Replicate matrix spike preparations (n = 4) at this level were determined with a high level of accuracy (89.8%) and precision (6.9% RSD). Replicates (n = 36) of a certified reference material (DOLT-2, trace metals in dogfish liver) were prepared and analyzed over a four year period in order to assess the ruggedness and accuracy of the method. The average recovery for mercury in this material was 99.9% of the certified level.
Electronic computers facilitate greatly carrying out factor analysis. Computers will help in solving the communality problem and the question of the number of factors as well as the question of arbitrary factoring and the problem of rotation. "Cloacal short-cuts will not be necessary and the powerful methods of Guttman will be feasible." A library of programs essential for factor analysis is described, and the use of medium sized computers as the IBM 650 deprecated for factor analysis. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
The popular concept of enrichment factors (EFs) as a means of identifying and quantifying human interference with global element cycles is evaluated. It is demonstrated that the concept of normalizing element concentrations to an average total crust value is of doubtful merit, for theoretical considerations alone. Serious flaws with EFs include the variable composition of the Earth's crust at any given point compared to the global average, the natural fractionation of elements during their transfer from the crust to the atmosphere through processes such as weathering and winnowing of fines, and the differential solubility of minerals in the weak chemical digestions generally used in environmental studies. Furthermore the impact of biogeochemical processes is neglected. A biomonitoring survey of atmospheric chemistry over a 1.5 million km2 area in northern Europe is used to show that EFs are governed here by completely different processes than anthropogenic activities. As a simple means to assess the maximum possible interference of human activities with global element reservoirs, the mining interference factor (MIF = (total tonnage mined annually/total tonnage in upper 2 km of crust) × 100%) is introduced. The elements C Br > Cu > Sb Ag > Cd > Pb show the highest MIFs, while Ga, Cs, Ge, K, In, I, and Rb show very low MIFs. We recommend indiscriminate usage of EFs in the scientific literature be abandoned and more large-scale surveys be supported internationally to collect quality, statistically significant environmental data. Only thus can human interference with natural biogeochemical cycles be properly documented.