Uptake and loss of technetium-95m in the crab Pachygrapsus marmoratus

The uptake and loss kinetics of ^95mTc in seawater have been investigated in the crab Pachygrapsus marmoratus. Both the uptake and loss kinetics can be represented as the sum of two exponential functions, one short-term ($\text{tb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 16}\text{d}$) and one long-term ($\text{tb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 63}\text{d}$), $\text{tb}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ being the biological half-time. The predicted steady state concentration factor was estimated to be about 18.No significant linear correlation between Tc uptake rate and animal weight was found during the accumulation phase. At the end of this phase, 77% of the Tc was found to be distributed in the digestive system and particularly in the hepatopancreas (56%); this organ also appeared to lose the radionuclide most quickly. During the loss phase, 90% of the incorporated radioactivity was eliminated in about three months. Therefore P. marmoratus does not appear to be a good bioindicator of Tc in the marine environment nor an important pathway for Tc contamination along marine food chains.     

Threshold and dose response estimation using the “filter model”

The “filter model” has been developed to explain the biologic effects of radiation and chemicals. We have examined nearly 300 sets of dose response data, of which 50 are presented here. Responses (induced by radiation and chemicals) which have been examined include in vitro survival studies on animal and plant tissues, induction of cellular aberrations and time to tumor or death. Similar data from in vivo studies has also been examined. All of the data appear to fit the model R = a lnD + b(lnD)² + c, where R is the response, a and b are parameters fitted by regression to a particular set of data, and c is the response at zero (or lowest) dose. By writing this model in exponential form, it can be seen that the response R results from multistage filtering (by net amounts a and b) of the initial dose, D. The threshold is obtained from this model as the point, $\text{D}\text{?}{}_{\mathrm{T}}$, at which the second derivative becomes zero. This is given by $\text{D}\text{?}{}_{\mathrm{T}}\text{=}\text{exp}\text{(1 ?}\text{a}\text{2b}\text{)}$ when a and b are oppositelt signed.     

Determination of 99Tc, 63Ni and 121m+126Sn in the marine environment

Four artificially produced radionuclides (${}^{99}\text{Tc, t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 2·15 × 10}{}^5\text{y;}{}^{63}\text{Ni, t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 93 y}$ and ${}^{\mathrm{121m+126}}\text{Sn, t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 55·5 y}$) have been analyzed in sediments and organisms from the marine environment. The samples were obtained from the vicinities of nuclear energy facilities, at sites of nuclear weapon tests and at sites remote from both of these locales. The activities of these nuclides per unit dry weight are remarkably similar at the first two of the above areas but are usually detectable only with difficulty, if at all, in the third area. Techniques for sample treatment and measurement are given.     

Experimental studies on the bioaccumulation of plutonium from sea water and a deep-sea sediment by clams and polychaetes

The bioavailability of ²³⁷Pu in the (III + IV) and (V + VI) oxidation states from sea water and a NE Atlantic deep-sea sediment has been studied for clams (Venerupis decussata) and polychaete worms (Hermione hystrix). After 22 days' exposure in sea water transfer factors (TF) had not reached equilibrium, and were 74 ± 5 and 61 ± 1 for clams and 370 ± 10 and 275 ± 11 for polychaetes, for Pu (III + IV) and Pu (V + VI) respectively. Depuration rates after sea water exposure followed a single exponential form ($\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 50}\text{days}$) for clams, and for polychaetes at least a two component from with $\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 1·3}\text{days}$ and 54 days. TF values for ²³⁷Pu bioaccumulation from sediments were very low, 6 × 10^?3 and 5 × 10^?2 for clams and polychaetes, respectively, after 20 days' exposure.Plotonium appears to be about 50% more bioavailable to the same species than americium as measured by laboratory experiments using a similar deep-sea sediment. Depuration experiments with clams after 40 days' exposure to labelled sediment indicated loss followed a single exponential form with a $\text{T}{}_{\mathrm{<mtext>b</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{= 24}\text{days}$. Significant differences in the behaviour of Pu introduced into the uptake and loss experiments in different oxidation states were not observed in general.     

Air-to-vegetation transfer rates of natural submicron aerosols

Submicron aerosol deposition to outdoor vegetation was evaluated by measuring vegetation and air concentrations of ²¹²Pb, ²¹⁴Pb, and ⁷Be attached to atmospheric aerosols. A biomass-normalized deposition velocity (V_D), with units of m³ kg^?1 s^?1, was used to compare species and isotopes with respect to air-to-vegetation transfer rates. For ²¹²Pb ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 10·64 h}$), higher night-time air concebtrations dominate deposition, while for ²¹⁴Pb ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 26·8}\text{min}$), deposition measurements over shorter time periods relative to changing atmospheric conditions were possible. Calculated V_D values were usually higher for ²¹⁴Pb, possibly reflecting wind-enhanced deposition during the afternoon period of sampling. Evergreen species, including pines, were not appreciably different from deciduous species. Most striking was the narrow range of results (factor of 6 for 34 ²¹²Pb measurements of 20 species). Beryllium-7 ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 53·3 d}$) was used to evaluate time-integrated deposition by sampling vegetation in California near the end of dry summers. Similar deposition rates were found for this isotope. The results of the study indicated that naturally radioactive atmospheric aerosols can be used to understand the dynamics of submicron aerosol deposition to ecosystems.     

Comparing computing formulas for estimating concentration ratios

The purpose of this paper is to provide guidance on the choice of computing formulas (estimators) for estimating average concentration ratios and other ratio-type measures of radionuclides and other environmental contaminant transfers between ecosystem components. Mathematical expressions for the expected value of three commonly used estimators (arithmetic mean of ratios, geometric mean of ratios, and the ratio of means) are obtained when the multivariate lognormal distribution is assumed. These expressions are used to explain why these estimators will not in general give the same estimate of the average concentration ratio. They illustrate that the magnitude of the discrepancies depends on the magnitude of measurement biases, and on the variance and correlations associated with spatial heterogeneity and measurement errors. This paper also reports on a computer simulation study that compares the accuracy of eight computing formulas for estimating a ratio relationship that is constant over time and/or space. Statistical models appropriate for both controlled spiking experiments and observational field studies for either normal or lognormal distributions are considered. Our results indicate that for either type of study the geometric mean is generally preferred if the lognormal distribution applies. However, the geometric mean has the disadvantage that its expected value depends on n, the number of measurements taken. Ricker's estimator, $\text{R}\text{?}{}_{\mathrm{rt}}$, appears to perform worse than the other estimators studied when the observations are lognormal. All eight estimators appear to be equally accurate for the controlled spiking study when data are normally distributed. For observational field studies when data are normally distributed the ratio of means or slight modifications thereof are preferred to other estimators investigated. Before one chooses a computing formula for estimating a concentration ratio, thought should be given to what target value needs to be estimated to satisfy study objectives, and to whether the normal or lognormal distribution is a more realistic model. The geometric mean performs well for lognormal distributions, but comparison of geometric means or of a geometric mean with environmental limits can be misleading if n is small. The arithmetic mean of ratios is a conservative choice in that it will always give a larger estimate than will the geometric mean. It may also be severely biased when data are lognormal and the variances of measurement errors are large. The ratio of the means is a reasonable choice if the distribution is normal. The median of the observed ratios, $\text{R}\text{?}{}_{\mathrm{<mtext>md</mtext>}}$, is useful estimate since it is easily obtained and has an easily understood interpretation as the point above which and below which 50% of the observed ratios lie. Also, it is appropriate no matter what the distribution of the observed ratios may be. Confidence limits on the median are also easily obtained. Finally, while this paper emphasizes applications in radionuclide research, our results should be applicable to a wide range of environmental contaminants since many contaminants have approximately lognormal distributions.     

Statistical assessment of subsampling procedures

As shown by the examples in this paper, the concentrations in subsamples are not necessarily independently and normally distributed despite vigorous grinding and mixing of the original sample. Studies of the statistical properties of subsample concentrations should test for deviations from independence and normality and, if deviations are found, should model the observed distribution. The tests include an analysis of variance to check for less variation among nearby subsamples than among widely spaced subsamples, as well as the computation of the probability plot correlation coefficient to check for nonnormality. These tests are illustrated with ${}^{239}\text{Pu}\text{+}{}^{240}\text{Pu}$ measurements on subsamples prepared for use as standard reference materials. These materials are used in quality assurance for environmental radioactivity measurements. The material consisting of Human Liver (SRM 4352) exhibits dependence, which may be due to inadequate mixing or to later handling that caused segregation. The material consisting of Human Lung (SRM 4351) and the material consisting of soil from Rocky Flats (SRM 4353) exhibit nonnormality due to the particulate nature of some plutonium-bearing fractions of the material. The lung measurements are modeled with the gamma distribution. The soil measurements are modeled with a combination of the normal distribution and a distribution that models the occurrence of outliers. The use of these models to describe the subsamples involves assessment of the contribution of the measurement error.     

Effects of drought stress on leaf gas exchange and chlorophyll fluorescence of Glycyrrhiza uralensis

Leaf gas exchange and chlorophyll fluorescence of Glycyrrhiza uralensis Fisch at two water supplies (equivalent to 240 mm for present precipitation and to 120 mm for future decreasing precipitation) were compared. There was a midday depression in net photosynthetic rate (P _N) for either treatment, but stomatal limitation was dominant for present precipitation treatment and non-stomatal limitation for the drought treatment. Compared with present precipitation treatment, P _N, stomatal conductance (g _s) and transpiration rate (E) were always lower at drought stress, but stomatal limitation value (L _s) and water use efficiency (WUE) were higher in the morning. The decrease in carboxylation efficiency (CE), apparent quantum yield (AQY), light-saturated photosynthetic rate and maximal photochemical efficiency of photosystem 2 (PS 2) (F _v/F _m) suggested that rubisco activity reduced and PS 2 partially inactivated during the day under drought. However, part of this inactivation of PS 2 might be alleviated due to increased thermal dissipation under drought.     

Variations in breeding success and daily nest survival of Whiskered Tern (<Emphasis Type="Italic">Chlidonias hybrida</Emphasis>) at two Iranian colonies

Variations in breeding success of the Whiskered Terns (Chlidonias hybrida) were studied in two wetlands; Anzali (2005 and 2008) and Zarivar (2007–2008) in north and west Iran. Nesting success was modeled and compared using information-theoretic approach implemented in program Mark in order to assess effects of colony locations, years and nest initiation dates on the probability of daily nest survival. Clutch size did not vary between colonies and years. Breeding success varied between colonies (Zarivar > Anzali), and years only in Anzali (2005 > 2008). Overall daily nest survival was 0.977. (95% LCI 0.973, UCI 0.981), equivalent to a Mayfield nest survival of 0.317. (95% LCI 0.255, UCI 0.387). Egg-laying periods and colony site were important covariates affecting the daily survival rates (Σω _i = 0.86 and Σω _i = 0.83, respectively), while, the support for the effect of year was less (Σω _i = 0.41). We concluded that Lake Zarivar provides a more favorable nesting location for Whiskered Terns probably because of little changes in rainfall and water depth during the breeding seasons which influence breeding performance.     

Krypton-85 in the atmosphere 1950–1977: a data review

For over 20 years the radioactive noble gas ⁸⁵Kr, the product of nuclear industry, has been released to the environment mainly from nuclear fuel reprocessing plants. Owing to its relatively long half-life $\text{T(}\text{1}\text{2}\text{= 10.76}\text{y}\text{)}$ and the absence of other appreciable sinks, a cumulative buildup of ⁸⁵Kr in the atmosphere is observed. The mean ⁸⁵Kr surface air activity in the northern hemisphere has increased from about 20 dpm/mmol Kr in 1950 to about 750 dpm/mmol Kr in 1977. In recent years, a substantial slow-down of the ⁸⁵Kr emission rate to the atmosphere has been observed. The published data indicate rather good mixing of ⁸⁵Kr in the northern hemisphere, but a gradient is observed in the southern hemisphere due to the fact that all nuclear fuel reprocessing plants are situated in the northern hemisphere and due to poor mixing of the atmosphere in the meridional direction.This paper summarizes nearly all of the data on ⁸⁵Kr activity in the atmosphere published up to the middle of 1978. The spatio-temporal distribution of ⁸⁵Kr atmospheric activity is discussed. Some forecasts of future ⁸⁵Kr concentration in the atmosphere and its possible ecological consequences are also presented.     

Characteristics of oxidant precursor emissions from anthropogenic sources in the United States

Hydrocarbons (HC) and nitrogen oxides (NO_x) have been identified as the most important precursor pollutants for oxidant formation in the atmosphere. These pollutants are emitted both from natural and anthropogenic sources; however, these two types of sources are generally geographically separated. Anthropogenic emissions are dominant in and around urban centers, where the majority of severe oxidant problems occur. Based on data gathered by the MAP3S/RAINE emissions inventory project, anthropogenic emissions of HC in the conterminous United States were 24.8 million metric tons in 1979. HC emissions were predominantly from area sources, the transportation sector being the largest contributor with 39.8% of the total. State-by-state breakdowns are also included. Based on analyses by other emissions inventory projects, the nonreactive fraction of the emissions from the transportation sector is less than 20% by weight. The highest proportion of HC emissions occur at low altitudes (0–50 m range) in high population density areas. Anthropogenic emissions of NO_x were 23.7 million metric tons in 1979; 50.8% were from point sources. The transportation sector and the electric utilities sector account for 37.1% and 30.9% of the NO_x emissions, respectively. The NO₂ fraction of the emissions from the transportation and electric utilities sectors is less than 10% by weight, based on NO/NO₂ speciation data from two other emissions inventories. Highest rates of NO_x emissions occur in high population density areas and are released at low altitude (0–50 m); three areas of high electric generating capacity were found to have high release altitudes.