On conditional skewness with applications to environmental data

The statistical literature contains many univariate and multivariate skewness measures that allow two datasets to be compared, some of which are defined in terms of quantile values. In most situations, the comparison between two random vectors focuses on univariate comparisons of conditional random variables truncated in quantiles; this kind of comparison is of particular interest in the environmental sciences. In this work, we describe a new approach to comparing skewness in terms of the univariate convex transform ordering proposed by van Zwet (Convex transformations of random variables. Mathematical Centre Tracts, Amsterdam, 1964), associated with skewness as well as concentration. The key to these comparisons is the underlying dependence structure of the random vectors. Below we describe graphical tools and use several examples to illustrate these comparisons.     

Growth and production of new recruits and adult individuals of Ascophyllum nodosum in a non-harvested population at its southern limit (Galicia,NW Spain)

Populations near the geographic distribution limits of the species are considered to live under suboptimal conditions, and hence, slight environmental changes can be critical for their survival. The potential sensitivity to disturbances of the long-living macroalga Ascophyllum nodosum was analyzed by the determination of growth, recruitment, mortality, and production of biomass of a population near its southern distribution limit. Recruitment, survival and growth rates of <2 years old individuals were determined in a new population growing in experimentally denudated squares. Demographic data for >2 years old individuals were obtained from individuals in the original population after estimating their age from the number of gas bladders in the thallus. Growth and survival were described as continuous nonlinear functions of age applied to the population and were further used to make demography-based production estimates. Recruitment of A. nodosum in denudated substrates seemed to require a previous cover of other macroalgae (as Fucus vesiculosus) as the only cohort detected during the 26-month period of the study was observed after F. vesiculosus individuals started to increase. The low production estimates (2,033 g m^?2 for a 10 year period) and poor recruitment may indicate a slow recuperation of this population to denudation. However, the large variability observed in the estimated growth curves of different populations along this southern distribution area suggests a large influence of local conditions that may help to overcome environmental changes at regional scales.     

Evaluating the main sources of groundwater pollution in the southern Tehran aquifer using principal component factor analysis

Determining the main sources of pollution (MSP) in groundwater is crucial to improve water quality (WQ) status. Field studies were conducted in this research, where five sampling campaigns were carried out from 36 wells in the southern Tehran aquifer. In all samples, WQ parameters were measured and evaluated regarding the Iranian drinking water standard (IDWS). Finally, by using the principal component factor analysis (PCFA), the probable MSP in the aquifer were determined. The results showed that all ions, total hardness, and total dissolved solids were above the IDWS. To analyze the PCFA results, only the first four of twenty rotated principal factors (RPFs) that conserved a high percentage of the variance of the data (about 90%) were considered. The results of the first PRF revealed that the geological structure was the MSP in the aquifer. Furthermore, the second RPF was mainly affected by nutrients (nitrate and orthophosphate) and microbial parameters (fecal and total coliforms), indicating the importance of agricultural activities and sewage effluents as another MSP in the aquifer. Finally, the remarkable share of heavy metals and pH in formation of the third and fourth RPFs, respectively, reflected the role of industrial activities as a probable MSP of groundwater.     

Biogeochemical characterization of surface waters in the Aljustrel mining area (South Portugal)

Aljustrel mining area (South Portugal) is a part of the Iberian Pyrite Belt and encloses six sulfide mineral masses. This mine is classified of high environmental risk due to the large tailings’ volume and acid mine drainage (AMD)-affected waters generated by sulfides’ oxidation. The use of biological indicators (e.g., diatoms) revealed to be an important tool to address the degree of AMD contamination in waters. Multivariate analysis has been used as a relevant approach for the characterization of AMD processes. Cluster analysis was used to integrate the significant amount and diversity of variables (physicochemical and biological), discriminating the different types of waters, characterized by the high complexity occurring in this region. The distinction of two main marked phenomena was achieved: (1) the circumneutral-Na-Cl water type (sites DA, PF, BX, BF, RO, CB), expressing the geological contributions of the Cenozoic sediments of Sado river basin, with high diatom diversity (predominating brackish diatoms as Entomoneis alata); and (2) the acid–metal-sulfated water type (sites BM, JU, RJ, AA, MR, BE, PC, AF), reflecting both the AMD contamination and the dissolution of minerals (e.g., silicates) from the hosting rocks, potentiated by the extremely low pH. This last group of sites showed lower diatom diversity but with typical diatoms from acid- and metal-contaminated waters (e.g., Pinnularia aljustrelica). In addition to these two water types, this hierarchical classification method also allowed to distinguish individual cases in subclusters, for example, treated dams (DC, DD), with alkaline substances (lime/limestone), that changed the physicochemical dynamics of the contaminated waters.

     

Glutathione S-tranferases and cytochrome P450 activities in Mytilus galloprovincialis from the South coast of Portugal: effect of abiotic factors

To assess the health of aquatic organisms, biomarkers that measure changes at the biochemical level have been used as effective early warning tools in ecological risk assessment. In order to develop an integrated risk assessment strategy for the south coast of Portugal, mussels Mytilus galloprovincialis were collected from six sites along the coast with different organic contaminant characteristics. Additionally, an active biomonitoring approach was followed by transplanting indigenous mussels from site 4 to 6 and vice versa (from site 6 to 4) for 28 days. PAHs and PCBs contents were measured and the associated responses of phase I and phase II detoxification mechanisms evaluated by measuring cytochrome P450 and GST activities. GST activity was also determined on different tissues (gills, digestive gland, foot, mantle and gonads) of M. galloprovincialis and the impact of abiotic parameters (temperature, salinity, pH, conductivity and dissolved oxygen) on the GST activity assessed. Results indicate that CYP 450 follow the same pattern of PAHs and a direct relationship exist between CYP 450 and PAH levels from the different sites. Although there is a decrease between GST and PAHs concentrations it was not significant. The majority of the GST activity was in the gills and the digestive gland (around of 75% of the activity measured in all tissues) followed in decreasing order by the mantle, gonads. An inverse relationship between GST activity and salinity was detected along with temperature although not significant. These two biomarkers respond to changes of these two groups of compounds and to salinity especially for GST. In conclusion CYP 450 in mussels gives a reliable response as biomarker for organic contaminants in risk assessment in the South Coast of Portugal.     

Fate of HTO following its acute soil deposition at different growth stages of Chinese cabbage

Lysimeter experiments were carried out in a greenhouse to study the fate of HTO following its soil deposition at different growth stages of Chinese cabbage. An HTO solution was applied to the surface of an acidic sandy soil at a time before, and four different times after, sowing. The transfer of HTO to the plants was quantified with the areal transfer factor (TFa, m2 kg(-1)-fresh) defined as the ratio of the plant concentration at harvest to the areal activity deposition. In the four post-sowing applications, the TFa values were in the ranges of 1.6 x 10(-5)-4.9 x 10(-3) for TFWT and 4.5 x 10(-6) -4.3 x 10(-5) for OBT, increasing with a decrease in the time interval between application and harvest. In the pre-sowing application, which was followed by a soil mixing, the TFa values for TFWT and OBT were 1.3 x 10(-4) and 8.6 x 10(-6), respectively. One week after harvest, soil samplings were made for the applications at 26 (A(26)) and 63d (A(63)) after sowing. Peaks of the depth profiles of the soil HTO appeared in the 10-15 cm layer for A(26) and the 5-10 cm layer for A(63). The top 30 cm of soil contained 0.5% and 20% of the applied activity for A(26) and A(63), respectively. Negligible fractions seemed to be in the deeper zone. It was estimated that almost all or most of the applied HTO had escaped to the air before plants' harvest.     

Screening ecological risk assessment of persistent organic pollutants in Mediterranean sea sediments

A screening ecological risk assessment (ERA) was conducted for the first time in the Mediterranean basin in order to assess the toxicity posed to the benthic community by PCBs, DDTs and HCB in marine sediments. The characterization of the exposure was conducted by means of an extensive literature survey, generating a database with more than 2000 samples. The effects were assessed by the adoption of guidelines previously developed in the literature, because ecotoxicological information about persistent organic pollutants (POPs) in the Mediterranean sediments was lacking. Existing sediment quality guidelines (SQGs) for the target pollutants were compiled and consensus values were calculated for three different categories of toxicity, namely threshold effect concentration (TEC), probable effect concentration (PEC) and extreme effect concentration (EEC). The combination of exposure and effects characterization enabled the identification of some areas of concern in the vicinity of industrial and urban locations and in the mouths of the main Mediterranean rivers. Beyond the Mediterranean continental shelf, the level of toxicity for the benthic community was generally low. The evaluation of the toxicity induced by the mixture of the target pollutants spotted the importance of DDT contamination in the Mediterranean sediments, despite the fact that main inputs to the sea have been significantly reduced during the last decades.     

Dose estimation and radon action level problems due to nanosize radon progeny aerosols in underground manganese ore mine

One of the essential parameters influencing of the dose conversion factor is the ratio of unattached short-lived radon progeny. This may differ from the value identified for indoor conditions when considering special workplaces such as mines. Inevitably, application of the dose conversion factors used in surface workplaces considerably reduces the reliability of dose estimation in the case of mines.This paper surveyed the concentration of radon and its short-lived radon progeny and identified the unattached fraction of short-lived radon progeny. As well equilibrium factor during the month of August was calculated simultaneously at two extraction faces in a manganese ore mine.During working hours the average radon concentrations were 220 Bq m⁻³ and 530 Bq m⁻³ at Faces 1 and 2; the average short-lived progeny concentration was 90 Bq m⁻³ and 190 Bq m⁻³, the average equilibrium factors were 0.46 and 0.36, and the average unattached fractions were 0.21 and 0.17, respectively. The calculated dose conversion factor was between 9 and 27 mSv WLM⁻¹, but higher values could also be possible.     

Spirometric tests to assess the prevalence of childhood asthma at Portuguese rural areas: influence of exposure to high ozone levels

The study here reported aimed to: i) evaluate the prevalence of childhood asthma at a Portuguese rural area with high ozone concentrations through lung function tests, validating the previously estimated one assessed through questionnaires (similar to those of the ISAAC); ii) compare the achieved prevalence with the one reported at an unexposed area (with low ozone concentrations), aiming to evaluate the influence of exposure to high ozone levels; and iii) determine potential risk factors. Ninety-five of the original 478 children that completed the questionnaires, mentioned to have at least one of asthma symptoms (wheeze, dyspnea or cough) and were therefore evaluated by spirometry. FEV(1) was in average 89.7% for asthmatics and 102.8% for non-asthmatics. For the studied sample the risk was higher for girls with a tendency to be higher from 8 to 10 years old. Lifetime prevalence of childhood asthma at the exposed area was 9.2%. Children living at the exposed area had 3 times higher risk of having asthma than those living at the unexposed area. Considering that ozone concentrations were the main difference between both areas, it can be suggested that ozone pollution increased asthma prevalence. Nevertheless, it should be remarked that further studies should be done to confirm these results.