Contributions of deposited particles to pine needle polycyclic aromatic hydrocarbons

The contributions of deposited particles (P) to polycyclic aromatic hydrocarbon (PAH) levels in pine (Cedrus deodar) needles sampled from the Dalian region were evaluated by washing off the particles from pine needle surfaces. P values ranged from 4.4 +/- 2.2% for fluorene to 69.9 +/- 4.0% for indeno(1,2,3-cd)pyrene, and positively correlated with the logarithm of octanol-air partition coefficients (log K OA) of each PAH significantly. P and the total levels of 14 PAHs under study ( summation PAHs), that ranged from 490 to 3241 ng g(-1) dw (dry weight) with median value of 1521 ng g(-1) dw, were high for traffic areas, and low for residential or park areas, implying the significant contributions of PAHs in both gas and particle phases emitted by vehicles. However, PAH profiles in pine needles were not significantly altered by the washing, due to the low fractions (2-5%) of the 5- and 6-ring PAHs in summation PAHs. The high wind speed and frequently alternating wind directions in the Dalian spring could quicken the depuration processes of pine needle PAHs. Thus, the local meteorological conditions and source variations should be taken into account when using pine needles to implicate seasonal variations of atmospheric semi-volatile organic compounds.     

Monitoring of heavy metals uptake and allocation in Pinus sylvestris organs in alkalised soil

The concentration of heavy metals in soil and in Scots pine (Pinus sylvestris) organs growing on a pH gradient from 4.0 to 7.9 of soil at different distances from a cement plant was monitored. Emission for over 40 years of alkaline dust (pH 12.3-12.6) into the atmosphere in North Estonia had resulted in alkalisation and elevated concentration of total heavy metals in upper layers of the soil (0-30 cm), which was considerable even 10 years after the dust pollution stopped. Monitoring showed that the accumulation and allocation of heavy metals varied between the stem, shoots and needles and differed from the trees in the unpolluted area, depending more on the mobility of elements and the pH than element concentrations in the alkaline soil. A strong negative correlation was found between the soil pH and Mn, Zn and Cd concentrations in different tree organs. Compared to the unpolluted area, Pb was present in relatively higher concentrations in all organs but Cr, Fe and Cu in needles and shoots. The concentrations of Mn and Cd were much lower than control in all organs of trees in alkalised soil. The height increment and density of needles on shoots were predominantly in negative correlation with the pH of soil.     

青岛市松针中多环芳烃污染状况研究

松针、苔藓类等植物可有效的监测环境空气中多环芳烃等有机污染物。为了解青岛市松针中多环芳烃的污染状况，本文使用索氏提取、氧化铝-硅胶净化柱净化、气相色谱-质谱（GC-MS）分析的方法，研究了青岛市6个不同区域的松针中多环芳烃的含量。该方法的提取净化效率在70．8％以上。在6个采样点中，1号采样点松针中的多环芳烃含量最低，平均为7．54ng/g（湿重含量），5号和6号采样点最高，分别为41．0ng/g和39．6ng/g。多环芳烃浓度季节变化规律为春季〉冬季〉夏季；松针中三、四环多环芳烃占总量的82％～90％，苯并（a）芘与多环芳烃总量具有较好的相关性。     

Short-term responses of soil chemistry, needle macronutrients and tree growth to clinker dust and fertiliser in a stand of Scots pine

Waste management of clinker dust by spreading it on forest soil was studied in a 25-year-old Scots pine stand on acidic sandy soil. Clinker dust (0.5 kg m?2), fertiliser (N, P, K, Mg, 0.05 kg m?2; N 190 kg ha?1) and untreated soil were applied on 120-m2 plots in four replicates. The fertiliser was included to confirm the nutrient limitation in the stand. Clinker dust increased the soil pH by 1.2 units relative to the pH of 4.6 in the untreated soil by the second year. Soil K and Mg concentrations were larger in the dust and fertiliser treatments. Nutrient diagnostics indicated that needles of untreated trees were deficient in N and K. Fertiliser treatment indicated that the growth of trees was limited by N, since the fertiliser tended to increase needle K, N, N/P, needle dry mass and diameters of stem and shoots. By an auxiliary dataset, no effects of the dust and fertiliser on possible excess of the micronutrient Mn were observed. Clinker dust increased needle K concentration, but due to the N limitation, there was no increase in the growth of stems, branches, shoots and needles. It was concluded that in plots of 120 m2 application of clinker dust at a rate of 0.5 kg m?2 was safe for the 21-year-old Scots pine stand in this trial on an acid nutrient-poor sandy soil during 4 years after the treatment.     

Study on Size Distribution of Total Aerosol and Water-Soluble Ions During an Asian Dust Storm Event at Jeju Island, Korea

Soil dust particles transported from loess regions of the Asian continent, called Asian dust, highly influences the air quality of north-eastern Asia and the northern Pacific Ocean. In order to investigate the effects of these dust storms on the chemical composition of atmospheric aerosol particles with different size, measurements of size distributions of total aerosol and major ion species were carried out on Jeju Island, Korea during April 2001. Juju Island was chosen for the study because the levels of emissions of anthropogenic air pollutants are very low. A 5-stage cascade impactor was used to sample size-fractionated aerosol particles. Samples were analyzed for major water-soluble ions using Dionex DX-120 ion chromatograph. The average mass concentration of total aerosol was found to be 24.4 and 108.3 microg m(-3) for non-Asian dust and Asian dust periods, respectively. The total aerosol size distribution, measured during the non-Asian dust period, was bimodal, whereas the coarse particles dominated the size distribution of total aerosol during the Asian dust period. It was found that SO4(2-), NH4+ and K+ were mainly distributed in fine particles, while Cl-, NO3-, Na+, Mg2+ and Ca2+ were in coarse particles. Although SO4(2-) was mainly distributed in fine particles, during the Asian dust period, the concentrations in coarse particles were significantly increased. This indicates heterogeneous oxidation of SO2 on wet surfaces of basic soil dust particles. The NH4+ was found to exist as (NH4)2SO4 in fine particles, with a molar ratio of NH4+ to SO4(2-) of 2.37 and 1.52 for non-Asian dust and Asian dust periods, respectively. Taking into account the proximity of the sampling site to the sea, and the observed chloride depletion, coarse mode nitrate, during the non-Asian dust period, is assumed to originate from the reaction of nitric acid with sodium chloride on the surfaces of sea-salt particles although the chloride depletion was not shown to be large enough to prove this assumption. During the Asian dust period, however, chloride depletion was much smaller, indicating coarse nitrate particles were mainly produced by the reaction of nitric acid with surfaces of basic soil particles. Most chloride and sodium components were shown to originate from sea-salt particles. Asian dust aerosols, arriving at Jeju Island, contained considerable amounts of sea-salt particles as they passed over the Yellow Sea. Ca2+ was shown to be the most abundant species in Asian dust particles.     

西安城北地区秋季PM_(2.5)中的矿尘颗粒污染特征

采用单颗粒气溶胶飞行时间质谱仪(Single Particle Aerosol Mass Spectrometer,SPAMS)对西安市大气矿尘颗粒物进行连续12 d在线分析,共采集到107 425个同时含有正负质谱信息的矿尘颗粒,矿尘颗粒物占PM_(2.5)样本数的8.44%。结果表明,矿尘颗粒物的正离子碎片成分以Na~+、K~+、Al~+、Ca~+、CaO~+、Fe~+为主,同时还含有Pb~+等,负离子碎片成分以NO~-_2和NO~-_3为主,另外还含有HSO~-_4、SiO~-_3、HSiO~-_3、H(NO_3)~-_2等。在西安市大气细颗粒物中,矿尘颗粒物中贡献较大的几类(如含钙、含铁、铁氧颗粒物等)大多是老化的成分。将观测阶段采集到的矿尘颗粒纳入本地污染源谱进行来源分析,其主要来源为扬尘源、工业源、燃煤源和汽车尾气源等。     

Levels of polycyclic aromatic hydrocarbons and dibenzothiophenes in wetland sediments and aquatic insects in the oil sands area of Northeastern Alberta, Canada

An immense volume of tailings and tailings water is accumulating in tailings ponds located on mine leases in the oil sands area of Alberta, Canada. Oil sands mining companies have proposed to use tailings- and tailings water-amended lakes and wetlands as part of their mine remediation plans. Polycyclic aromatic hydrocarbons (PAHs) are substances of concern in oil sands tailings and tailings water. In this study, we determined concentrations of PAHs in sediments, insect larvae and adult insects collected in or adjacent to three groups of wetlands: experimental wetlands to which tailings or tailings water had been purposely added, oil sands wetlands that were located on the mine leases but which had not been experimentally manipulated and reference wetlands located near the mine leases. Alkylated PAHs dominated the PAH profile in all types of samples in the three categories of wetlands. Median and maximum PAH concentrations, especially alkylated PAH concentrations, tended to be higher in sediments and insect larvae in experimental wetlands than in the other types of wetlands. Such was not the case for adult insects, which contained higher than expected levels of PAHs in the three types of ponds. Overlap in PAH concentrations in larvae among pond types suggests that any increase in PAH levels resulting from the addition of tailings and tailings water to wetlands would be modest. Biota-sediment accumulation factors were higher for alkylated PAHs than for their parent counterparts and were lower in experimental wetlands than in oil sands and reference wetlands. Research is needed to examine factors that affect the bioavailability of PAHs in oil sands tailings- or tailings water-amended wetlands.     

Growth, aboveground biomass, and nutrient concentration of young Scots pine and lodgepole pine in oil shale post-mining landscapes in Estonia

The investigation was carried out in 8-year-old Scots pine (Pinus sylvestris L.) and lodgepole pine (Pinus contorta var. latifolia Engelm.) plantations on post-mining area, Northeast Estonia. The aim of the study was to assess the suitability of lodgepole pine for restoration of degraded lands by comparing the growth, biomass, and nutrient concentration of studied species. The height growth of trees was greater in the Scots pine stand, but the tree aboveground biomass was slightly larger in the lodgepole pine stand. The aboveground biomass allocation to the compartments did not differ significantly between species. The vertical distribution of compartments showed that 43.2% of the Scots pine needles were located in the middle layer of the crown, while 58.5% of the lodgepole pine needles were in the lowest layer of the crown. The largest share of the shoots and stem of both species was allocated to the lowest layer of the crown. For both species, the highest NPK concentrations were found in the?needles and the lowest in the stems. On the basis of the present study results, it can be concluded that the early growth of Scots pine and lodgepole pine on oil shale post-mining landscapes is similar.     

Environmental monitoring of heavy metals and arsenic from Ag-Pb-Zn mining: a case study over two millennia

2000 years of mining activity at Wiesloch, Germanyleft behind a legacy of mining wastes, some of which haveextremely high contents of toxic elements like As, Cd, Tl,Sb, Pb and Zn. To evaluate their long-term impact ondifferent environmental compartments, the detailedenvironmental monitoring presented here focused on themineralogical and chemical characterization of thedifferent waste materials, consisting of dumpings with orefragments, flotation tailings and medieval metallurgicalslags. Leaching experiments with these materials, usingeluents of different compositions and pHs were carried outto assess the conditions governing the mobilization and re-fixation of these species. It was shown, that the carbonatehost rock of the mineralization, the loess blanket coveringthe area and the organically rich municipal sewage sludgesdeposited on top of the tailings, represent potentialbarriers to the dispersion of toxic elements over a muchlarger area. Moreover, particulate emissions from thesteep, unvegetated escarpments of the tailing heapsrepresent a continuous thread to the environment.     

Concentrations of sulphur and heavy metals in needles and rooting soils of Masson pine (Pinus massoniana L.) trees growing along an urban–rural gradient in Guangzhou, China

Current (C) and previous year (C + 1) needles and soils (organic horizon, 0-10 cm and 10-20 cm mineral depth) of Masson pine (Pinus massoniana L.) trees were sampled at four forested sites (Huang Pu industrial district, HP; South China Botanical Garden, BG; Mao Feng Mt., MF; and Nan Kun Mt., NK) in Guangzhou along a urban-rural gradient and analyzed for sulfur (S) and heavy metals (Cu, Zn, Ni, Cd, Cr and Pb) concentrations. Needle concentrations of all the elements were significantly higher at industrial HP than at other three sites, except for Cu and Pb which were highest at the traffic site (BG). The C + 1 needles generally had higher Cu, Cd, Pb, Zn, Cr than the C needles while the opposite was for Ni and S. Total and available Cd, Pb, Zn in soils peaked at the urban sites (HP and BG) and decreased at suburban MF and rural NK. Heavy metals were generally higher in the organic soils than in the mineral soils at all sites. Zinc and Pb at all sites, and Cd, S and Cu at the urban sites (HP and BG) in soils or pine needles were above or near their respective natural background levels, implying that threats resulted from these toxic elements occurred on local particularly urban forests, but did not for Cr and Ni due to their presence below their background values. Our results demonstrated that elements concentrations in needles and soils had reflected the variability of pollutants and the environmental quality change along the urban-rural transect, and were efficient as biomonitors to assess the influence of anthropogenic activities along the urbanization course on forest health.     

Possible markers of traffic-related emissions

Looking for robust indicators of motor vehicle emissions it has been found that brake wear and linings are significant contributors of Cu, Mo and Sb to air particulate matter. These trace elements, whose mutual ratios in airborne particulate matter resulted quite different from those in crustal material, appear to be available fingerprinting tools to identify the contribution of on-road vehicles to traffic-derived particulate matter. In this study, the results of analytical determinations of Cu, Mo and Sb on PM(10), PM(2.5), vegetation and brake dust samples, together with gas (CO, NOx) concentrations, are discussed. Highly significant correlations among Cu, Sb and Mo were observed in particulate matter from Palermo and between Cu-Sb and Cu-Mo at Catania. Further significant positive correlations have been found in pine needles from Palermo, Gela and in platanus leaves from Catania.     

Distribution of airborne particles from multi-emission source

The purpose of this work was to study the distribution of airborne particles in the surroundings of an iron and steel factory in southern Finland. Several sources of particulate emissions are lying side by side, causing heavy dust loading to the environment. This complicated multi-pollutant situation was studied mainly by SEM/EDX methodology.Particles accumulated on Scots pine bark were identified andquantitatively measured according to their element content,size and shape. As a result, distribution maps of particulateelements were drawn and the amount of different particle typesalong the study lines was plotted. Particulate emissions fromthe industrial or energy production processes were not themain dust source. Most emissions were produced from theclinker crusher. Numerous stockpiles of the industrial wastesand raw materials also gave rise to particulate emissions as aresult of wind erosion. It was concluded that SEM/EDXmethodology is a useful tool for studying the distribution ofparticulate pollutants.     

Detection of sulphur dioxide in the air using Scotch pine needles

Air quality is especially important in surface layers, for it is this layer that provides the living components of environment with the needed oxygen and carbon dioxide. Various air polluting gases penetrate cells affecting and contaminating them. Chloroplast shell of some pine species, for instance, doubles under the impact of carbon dioxide which is followed by tillacoids swelling and reduction.Literature provides opinions of some authors, who consider Scotch pine needle to be a biological indicator of sulphur dioxide. Others object to it basing on the observations of physiological development.The property of a Scotch pine as that of biological indicator manifests in SO₂ absorption by its needles. The analysis of total content of SO₂ in the needles shows an increase of SO₂ concentration.Sulphur in the needles is found in the form of organically bound sulphur, aminoacids, hormones as well as in the form of sulphates.Basing on our previous analysis we have generalized the data on the correlation concentrations of sulphur dioxide in the air and general concentrations of sulphur in the needles. We have supplemented the observations with the analyses of organically bound sulphur and concentrations of nonorganic sulphur. According to research data, needles contain a characteristic and rather stable quantity of organically bound sulphur.So we may state that the SO _inf4 ^sup2– concentration and the amount of SO₂ absorbed from the air are interdependent.Some authors state that SO _inf4 ^sup2– content in the soil doesn't affect sulphur content in pine needles. That is why we studied the affect of SO _inf4 ^sup2– content in the soil on sulphur content in Scotch pine needles.We could prove this statement by means of various kinds of analyses only partially. The ion transport is affected by the presence of other ions, pH and a lot of other factors.What may be said for sure is that different qualities of soils gave only minor and insignificant deviations.Hence our assumption about the SO₂ contamination from air, proved by its effect on the soils, turns to suit approximate measurements.     

Geochemical position of Pb,Zn and Cd in soils near the Olkusz mine/smelter,South Poland: effects of land use,type of contamination and distance from pollution source

The soils adjacent to an area of historical mining, ore processing and smelting activities reflects the historical background and a mixing of recent contamination sources. The main anthropogenic sources of metals can be connected with historical and recent mine wastes, direct atmospheric deposition from mining and smelting processes and dust particles originating from open tailings ponds. Contaminated agriculture and forest soil samples with mining and smelting related pollutants were collected at different distances from the source of emission in the Pb–Zn–Ag mining area near Olkusz, Upper Silesia to (a) compare the chemical speciation of metals in agriculture and forest soils situated at the same distance from the point source of pollution (paired sampling design), (b) to evaluate the relationship between the distance from the polluter and the retention of the metals in the soil, (c) to describe mineralogy transformation of anthropogenic soil particles in the soils, and (d) to assess the effect of deposited fly ash vs. dumped mining/smelting waste on the mobility and bioavailability of metals in the soil. Forest soils are much more affected with smelting processes than agriculture soils. However, agriculture soils suffer from the downward metal migration more than the forest soils. The maximum concentrations of Pb, Zn, and Cd were detected in a forest soil profile near the smelter and reached about 25 g kg^− 1, 20 g kg^− 1 and 200 mg kg^− 1 for Pb, Zn and Cd, respectively. The metal pollutants from smelting processes are less stable under slightly alkaline soil pH then acidic due to the metal carbonates precipitation. Metal mobility ranges in the studied forest soils are as follows: Pb > Zn ≈ Cd for relatively circum-neutral soil pH (near the smelter), Cd > Zn > Pb for acidic soils (further from the smelter). Under relatively comparable pH conditions, the main soil properties influencing metal migration are total organic carbon and cation exchange capacity. The mobilization of Pb, Zn and Cd in soils depends on the persistence of the metal-containing particles in the atmosphere; the longer the time, the more abundant the stable forms. The dumped mining/smelting waste is less risk of easily mobilizable metal forms, however, downward metal migration especially due to the periodical leaching of the waste was observed.     

Heavy metal concentrations in particle size fractions from street dust of Murcia (Spain) as the basis for risk assessment

Street dust has been sampled from six different types of land use of the city of Murcia (Spain). The samples were fractionated into eleven particle size fractions (<2, 2-10, 10-20, 20-50, 50-75, 75-106, 106-150, 150-180, 180-425, 425-850 μm and 850-2000 μm) and analyzed for Pb, Cu, Zn and Cd. The concentrations of these four potentially toxic metals were assessed, as well as the effect of particle size on their distribution. A severe enrichment of all metals was observed for all land-uses (industrial, suburban, urban and highways), with the concentration of all metals affected by the type of land-use. Coarse and fine particles in all cases showed concentrations of metals higher than those found in undisturbed areas. However, the results indicated a preferential partitioning of metals in fine particle size fractions in all cases, following a logarithmic distribution. The accumulation in the fine fractions was higher when the metals had an anthropogenic origin. The strong overrepresentation of metals in particles <10 μm indicates that if the finest fractions are removed by a vacuum-assisted dry sweeper or a regenerative-air sweeper the risk of metal dispersion and its consequent risk for humans will be highly reduced. Therefore, we recommend that risk assessment programs include monitoring of metal concentrations in dust where each land-use is separately evaluated. The finest particle fractions should be examined explicitly in order to apply the most efficient measures for reducing the risk of inhalation and ingestion of dust for humans and risk for the environment.     

Pine needles as sensors of atmospheric pollution

Neutron Activation Analysis of pine needles from trees growing in areas of relatively high and low airborne pollution has been performed. Needles of three different species, and from several sequential year's crops, have been studied. The purpose of the study was to determine the type of distribution governing the elemental concentrations, the inter-and intrasite differences, and the degree of dependence on soil vs airborne elemental sources. A log normal distribution was found for those elements considered to be well determined. The results indicate that pine needles can be used as an air pollution monitor provided that sufficient sampling is done to compensate for natural variation in elemental concentrations.     

Actinides and decay products in selected produce and bioindicators in the vicinity of a uranium plant

Cypress needles collected at the edge of the Malvési uranium facility (SW France) exhibit enhanced activities of actinides and some decay products (uranium, americium, plutonium, (230)Th, (226)Ra) compared to a remote site. These enhanced activities resulted from the release of U via smokestacks and passive release from former artificial ponds located inside the nuclear site. Enhanced activities are also observed in selected produce (wheat, lettuce, fruits) sampled from the edge of the site. However, excess actinides measured in wheat grains in 2007 are inconsistent with the activities and the uranium ratio measured in the soils. This result suggests that the studied annual crops were contaminated mainly through the short-term release of airborne actinides, and that other transfer pathways, such as, uptake through the roots or adhesion of soil particles, were negligible.     

Vertical gradients of mineral elements in Pinus sylvestris crown in alkalised soil

Alkalisation of soil has been assumed to be the principal cause of changes in vertical gradients of nutrients in Pinus sylvestris crown. The long-term influence of alkaline dust pollution ( ${\rm {pH}}_{{\rm H}_{2}{\rm O}}$  12.3–12.6) emitted from a cement plant on the element composition of soil and needles of Scots pine in different canopy layers was studied. In the polluted area, the pH of soils was >7, and high amounts of Ca, K and Mg were measured in the upper layers of soil (0–30 cm), while the mobility and solubility of some contaminants have decreased, nutrition processes have become complicated, and imbalance of mineral composition of trees was revealed. Reduced N and increased K, Ca and Mg concentrations in needles were observed in the heavily polluted area. Vertical gradients of elements and their ratios in canopies varied depending on the alkalisation level of soil. Needles on the upper-crown shoots had higher concentrations of N, C, Ca and Mg and lower concentrations of P and K compared to the lower layer of the crown. In the unpolluted area, higher concentrations of N, P, K and Ca were found in lower-crown needles and of C and Mg in needles at the top of the canopy. The P/N ratio below 0.125 indicated P deficiency in pines. The ratios N/Ca, N/Mg and N/K had significantly decreased, while the ratios Ca/Mg, K/Mg and K/Ca had a tendency to increase in heavily polluted sample plots. Magnitude of changes of element ratios indicates on the disbalances of availability and translocation of nutrients in the crown of trees.     

A comparison of the growth of Scots pine (Pinus sylvestris L.) in a reclaimed oil shale post-mining area and in a Calluna site in Estonia

The growth of Scots pine and its suitability for afforestation of post-mining landscapes in Northeast Estonia were assessed in comparative analytical studies by using morphological parameters and mineral nutrition characteristics. The growth and nutrient uptake of Scots pine growing on post-mining substrate were compared with the characteristics of pines of the same age (22–23 years) in a Calluna forest site type predominant in North Estonia in similar climatic zone. Results of the analyses of soil upper layers showed that the concentration of N and P in soil did not differ between the opencast spoil and Calluna site, but significantly higher pH of soil and concentrations of K, Ca, and Mg were found in mine spoil. The concentrations of K and Mg in needles were significantly higher in the post-mining area, but the concentrations of N, P, and Ca did not differ significantly. Comparison of the needle nutrient concentration with the standard for optimum concentrations revealed P deficit in the post-mining area and P and K deficit in the Calluna site. Scots pine formed longer and thinner needles and shoots in the post-mining substrate than in the Calluna site. It was assumed that in the post-mining area the growth of pines is predominantly dependent on K and Ca concentrations in their tissues as the biomass of needles was strongly correlated with the K/Ca ratio, whereas the biomass in the Calluna site was correlated with the N/P ratio. The height and diameter of trees were significantly larger in the post-mining area.     

Biological monitoring of wood dust exposure in nasal lavage by high-performance liquid chromatography

A high-performance liquid chromatography (HPLC) method for biomonitoring of occupational wood dust exposure based on nasal lavage as a biomonitoring matrix was developed. Gallic acid (GA) was chosen as the indicator compound for oak dust exposure. From the chromatographic profile of ash dust, four peaks were chosen as indicator compounds. Phenolic indicator compounds were analysed by HPLC. Personal dust samples and corresponding nasal lavage samples were collected from 16 workers exposed to oak dust and six to ash dust. The dust concentrations in the workers' breathing zone varied between 0.7 and 13.8 mg m(-3). The indicators revealed the nature of the wood dust inhaled. For the workers who did not use respirators, the correlation between the dust and corresponding indicator compound in their nasal lavage was significant; r2 = 0.59 (n = 12) for oak dust and r2 = 0.58 (n = 6) for ash dust, respectively. Further, the correlation for oak dust workers who used respirators was r = 0.67 (n = 4). Nasal lavage sampling and HPLC analysis of polyphenol indicator compounds are promising tools for measuring wood dust exposure. Although further validation is necessary, determination of the individual dose may prove invaluable in prospective epidemiological studies.