Internal cohesion and geometric shape of spatial clusters

The geographic delineation of irregularly shaped spatial clusters is an ill defined problem. Whenever the spatial scan statistic is used, some kind of penalty correction needs to be used to avoid clusters’ excessive irregularity and consequent reduction of power of detection. Geometric compactness and non-connectivity regularity functions have been recently proposed as corrections. We present a novel internal cohesion regularity function based on the graph topology to penalize the presence of weak links in candidate clusters. Weak links are defined as relatively unpopulated regions within a cluster, such that their removal disconnects it. By applying this weak link cohesion function, the most geographically meaningful clusters are sifted through the immense set of possible irregularly shaped candidate cluster solutions. A multi-objective genetic algorithm (MGA) has been proposed recently to compute the Pareto-sets of clusters solutions, employing Kulldorff’s spatial scan statistic and the geometric correction as objective functions. We propose novel MGAs to maximize the spatial scan, the cohesion function and the geometric function, or combinations of these functions. Numerical tests show that our proposed MGAs has high power to detect elongated clusters, and present good sensitivity and positive predictive value. The statistical significance of the clusters in the Pareto-set are estimated through Monte Carlo simulations. Our method distinguishes clearly those geographically inadequate clusters which are worse from both geometric and internal cohesion viewpoints. Besides, a certain degree of irregularity of shape is allowed provided that it does not impact internal cohesion. Our method has better power of detection for clusters satisfying those requirements. We propose a more robust definition of spatial cluster using these concepts.     

The current status and environmental impacts of glyphosate-resistant crops: a review

Glyphosate [N-(phosphonomethyl) glycine]-resistant crops (GRCs), canola (Brassica napus L.), cotton (Gossypium hirsutum L.), maize (Zea mays L.), and soybean [Glycine max (L.) Merr.] have been commercialized and grown extensively in the Western Hemisphere and, to a lesser extent, elsewhere. Glyphosate-resistant cotton and soybean have become dominant in those countries where their planting is permitted. Effects of glyphosate on contamination of soil, water, and air are minimal, compared to some of the herbicides that they replace. No risks have been found with food or feed safety or nutritional value in products from currently available GRCs. Glyphosate-resistant crops have promoted the adoption of reduced- or no-tillage agriculture in the USA and Argentina, providing a substantial environmental benefit. Weed species in GRC fields have shifted to those that can more successfully withstand glyphosate and to those that avoid the time of its application. Three weed species have evolved resistance to glyphosate in GRCs. Glyphosate-resistant crops have greater potential to become problems as volunteer crops than do conventional crops. Glyphosate resistance transgenes have been found in fields of canola that are supposed to be non-transgenic. Under some circumstances, the largest risk of GRCs may be transgene flow (introgression) from GRCs to related species that might become problems in natural ecosystems. Glyphosate resistance transgenes themselves are highly unlikely to be a risk in wild plant populations, but when linked to transgenes that may impart fitness benefits outside of agriculture (e.g., insect resistance), natural ecosystems could be affected. The development and use of failsafe introgression barriers in crops with such linked genes is needed.     

Potentially toxic elements (PTEs) in soils from the surroundings of the Trans-Amazonian Highway,Brazil

The Trans-Amazonian Highway (TAH) is located in the northern region of Brazil, comprising a border region where agricultural, mining, and logging activities are the main activities responsible for fostering economic development, in addition to large hydroelectric plants. Such activities lead to environmental contamination by potentially toxic elements (PTEs). Environmental monitoring is only possible through the determination of element contents under natural conditions. Many extraction methods have been proposed to determine PTEs’ bioavailability in the soil; however, there is no consensus about which extractor is most suitable. In this study, we determined the contents of PTEs in soils in the surroundings of TAH after mineral extraction with diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA), Mehlich I, and Mehlich III solutions. Soil samples were collected in areas of natural vegetation in the vicinity of TAH in the state of Pará, Brazil. Chemical attributes and particle size were determined, besides concentrations of Fe, Al, Mn, and Ti by sulfuric acid digestion, Si after alkaline solution attack, and poorly crystalline Fe, Al, and “free” Fe oxides. Mehlich III solution extracted greater contents from Fe, Al, and Pb as compared to Mehlich I and DTPA-TEA and similar contents from Cd, Mn, Zn, and Cu. Significant correlations were found between concentrations of PTEs and the contents of Fe and Mn oxides as well as organic carbon and soil cation exchange capacity. Contents of Cu, Mn, Fe, and Zn by the three methods were positively correlated.     

Herbicide leaching on a recharge area of the Guarany aquifer in Brazil

The region of Ribeir?o Preto City, located in Southeast of Brazil, S?o Paulo State, is an important sugarcane, soybean, and corn producing area with a high level of pesticides utilization. This region is also an important recharge area for groundwater supply of the Guarany aquifer. Since the past ten years atrazine, simazine, ametryn, tebuthiuron, diuron, 2,4-D, picloram, and hexazinone are the main herbicides used in this area. In order to study a possible leaching of some of these herbicides into the aquifer, surface, and groundwater samples were collected in a watershed during the years of 1996 to 2003, from different locations. To detect and quantify the herbicides a GC-MS (gas chromatograph/mass spectrometry) method was used. The response of the herbicides analyzed was linear over the concentration range of 0.02 to 2.0 microg/L. Analysis of groundwater revealed that the herbicides tebuthiuron, diuron, atrazine, simazine, and ametryn were not present in the samples. In the surface water collected in 1997, ametryn was present in two out of nine locations with concentrations ranging from 0.17 and 0.23 microg/L, which is above the allowable 0.1 microg/L according to the European safety level. The leaching potential of tebuthiuron, diuron, atrazine, simazine, 2,4-D, picloram, and hexazinone has been evaluated using CMLS-94, "Chemical Movement in Layered Soil," as simulation model. No leaching into the depth of the water table at 40 m was found.     

Substance flows through the economy and environment of a region

In the tradition of the study of materials flows through society, the Substance Flow Analysis (SFA) method and its software tool SFINX are presented. SFA aims at providing the relevant information for a country’s overall management strategy regarding single substances or coherent groups of substances. Three modelling techniques and their possibilities and limitations are discussed: Bookkeeping, static modelling, and dynamic modelling. The computer program SFINX can be used for varoius purposes: (1) to obtain an overview of stocks and flows of a substance in, out and through a nation’s economy and environment for a specific year, (2) to trace the origins of specific pollution problems, and (3) to estimate the effectiveness of certain abatement measures. Each application has its own requirements with regard to data and modelling.     

Substance flows through the economy and environment of a region

Part I: Abstract  In the tradition of the study of materials flows through society, the Substance Flow Analysis (SFA) method is presented. SFA aims at providing the relevant information for a country’s overall management strategy regarding single substances or coherent groups of substances. This article is dedicated to the presentation of a threestep general framework for SFA-type studies, and elaborates on its first step the systems definition. Attention is given to the definition of the external and internal system boundaries, the categorization of the system’s elements, aspects of materials choice, time, and space, and how these depend on the aim of the conducted study. Moreover, a broader discussion is started on the need for standardization of materials flow studies in general. Part II: Abstract  In the tradition of the study of materials flows through society, the Substance Flow Analysis (SFA) method and its software tool SFINX are presented. SFA aims at providing the relevant information for a country’s overall management strategy regarding single substances or coherent groups of substances. Three modelling techniques and their possibilities and limitations are discussed: Bookkeeping, static modelling, and dynamic modelling. The computer program SFINX can be used for varoius purposes: (1) to obtain an overview of stocks and flows of a substance in, out and through a nation’s economy and environment for a specific year, (2) to trace the origins of specific pollution problems, and (3) to estimate the effectiveness of certain abatement measures. Each application has its own requirements with regard to data and modelling.     

Genetic sub-structure and intermediate optimal outcrossing distance in the marine angiosperm <Emphasis Type="Italic">Zostera marina</Emphasis>

The spatial distribution of genetic variability depends on the spatial patterns of clonal and sexual reproduction, gene flow, genetic drift and natural selection. Species with restricted dispersal may exhibit genetic structuring within populations with immediate neighbours being close relatives, and may show differentiation among populations. Genetic structuring of a species may have important genetic, evolutionary and ecological consequences including distance-dependent mating success. In this study we used microsatellite markers to show that clones of Zostera marina in a population in the Ria Formosa, Portugal, were aggregated and covered distances of up to 3–4 m. Clones within 4 m of each other exhibited significant and positive coancestry values, reflecting the limited seed dispersal of this species. Hand-pollinations between near (0–10.9 m), intermediate (11–32 m) and far (15 km) individuals resulted in similar levels of seed set, although the near pollinations had higher, although not statistically significant, levels of seed abortion during maturation. Seeds from intermediate-distance pollinations had a significantly higher proportion of seeds germinate and shorter germination time than both the near and far seeds. Similarly, the average number of seedlings produced per pollination, used as an overall estimate of fitness, was significantly greater for the intermediate distance when compared to both near and far pollinations. These results suggest that the genetic structuring observed may result in both inbreeding and outbreeding depression, which gives rise to an intermediate optimal outcrossing distance.     

Toxicity of the mixture of selected antineoplastic drugs against aquatic primary producers

The residues of antineoplastic drugs are considered as new and emerging pollutants in aquatic environments. Recent experiments showed relatively high toxicity of 5-fluorouracil (5-FU), imatinib mesylate (IM), etoposide (ET) and cisplatin (CP) that are currently among most widely used antineoplastic drugs, against phytoplankton species. In this study, we investigated the toxic potential of the mixture of 5-FU?+?IM?+?ET against green alga Pseudokirchneriella subcapitata and cyanobacterium Synechococcus leopoliensis, and the stability and sorption of these drugs to algal cells. Toxic potential of the mixture was predicted by the concepts of ‘concentration addition’ and ‘independent action’ and compared to the experimentally determined toxicity. In both test species, the measured toxicity of the mixture was at effects concentrations EC₁₀–EC₅₀ higher than the predicted, whereas at higher effect concentration (EC₉₀), it was lower. In general, P. subcapitata was more sensitive than S. leopoliensis. The stability studies of the tested drugs during the experiment showed that 5-FU, IM and CP are relatively stable, whereas in the cultures exposed to ET, two transformation products with the same mass as ET but different retention time were detected. The measurements of the cell-linked concentrations of the tested compounds after 72 h exposure indicated that except for CP (1.9 % of the initial concentration), these drugs are not adsorbed or absorbed by algal cells. The results of this study showed that in alga and cyanobacteria exposure to the mixture of 5-FU?+?ET?+?IM, in particular at low effect concentration range, caused additive or synergistic effect on growth inhibition, and they suggest that single compound toxicity data are not sufficient for the proper toxicity prediction for aquatic primary producers.     

Leaching and half-life of the herbicide tebuthiuron on a recharge area of Guarany aquifer in sugarcane fields in Brazil

This study was undertaken to evaluate the degradation and mobility of the herbicide tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) in soil under field conditions, and its potential for leaching and groundwater contamination. A watershed, Espraiado, located over a recharge area in Brazil, was chosen for soil and water studies. At Espraiado, water samples were collected from seven wells at intervals of three months from March 2004 to June 2006 and analyzed for tebuthiuron. Other samples were taken from city wells located outside of the recharge area. To assess the potential movement to the aquifer, tebuthiuron was also applied to trial plots at the recommended label rate of 1.0 kg/ha a.i. in May of 2004, with and without sugarcane coverage, on sandy soil. Soil samples were collected during the years of 2004 and 2005, at depths intervals of 20 cm from soil surface down to 120 cm and analyzed for tebuthiuron at zero, 3, 30, 60, 90, 120, 150, 180, 240, and 300 days after application. There was no clear effect of sugarcane coverage on the tebuthiuron degradation in soils, but it moved faster into the soil where there was no cover. After 180 days there were no measurable residues in the soil, and tebuthiuron was not found below 40 cm depth in any time. Tebuthiuron had a half-life of 20 days under those conditions. No tebuthiuron residue was found in ground water samples at any sampling time.     

Influence of humic fractions on retention of isoproturon residues in two Moroccan soils

The influence of different fractions of soil organic matter on the retention of the herbicide isoproturon (IPU) has been evaluated. Water and methanol extractable residues of ¹⁴C labeled isoproturon have been determined in two Moroccan soils by β -counting–liquid chromatography. The quantification of bound residues in soil and in different fractions of soil humic substances has been performed using pyrolysis/scintillation-detected gas-chromatography. Microbial mineralization of the herbicide and soil organic matter has been also monitored. Retention of isoproturon residues after 30-days incubation ranged from 22% to 32% (non-extractable fraction). The radioactivity extracted in an aqueous environment was from 20% to 33% of the amount used for the treatment; meanwhile, methanol was able to extract another 48%. Both soils showed quantities of bound residues into the humin fraction higher than humic and fulvic acids. The total amount of residues retained into the organic matter of the soils was about 65 % of non-extractable fraction, and this percentage did not change with incubation time; on the contrary, the sorption rate of the retention reaction is mostly influenced by the clay fraction and organic content of the soil. Only a little part of the herbicide was mineralized during the experimental time.