Aging of TiO2 nanocomposites used in sunscreen. Dispersion and fate of the degradation products in aqueous environment

Aging in water of a TiO₂-based nanocomposite used in sunscreen cosmetics has been studied as a function of light and time. It consisted initially in a TiO₂ core, coated with Al(OH)₃ and polydimethylsiloxane (PDMS) layers. Size measurement, coating alteration, and surface charge were followed by laser diffraction, TEM/EDS, ICP-AES and electrophoretic mobility measurement.The nanocomposite rapidly underwent progressive dispersion in the aqueous phase, enabled by the dissolution of the PDMS layer. A stable suspension of colloidal byproducts from 50 to 700 nm in size was formed. Their positively charged Al(OH)₃ surface was evidenced with an isoelectric point around 7-8, controlling the dispersion stability. The critical coagulation concentrations measured with NaCl and CaCl₂ was 2 × 10⁻² and 8 × 10⁻³ M respectively. The presence of natural organic matter affected the colloidal stability according to the NOM/byproduct ratio. A 2 wt% ratio favored bridging flocculation, whereas a 20 wt% ratio induced sterical stabilization.     

Fetal abdomino-perineal lymphangioma: differential diagnosis and management

Fetal lymphangiomas are rare congenital anomalies of the lymphatic system most commonly presenting in the head and neck. Cystic abdominal lymphangiomas are more rare with only a few cases reported prenatally. We report a case of a prenatally detected abdomino-perineal lymphangioma that mimicked the more fatal prenatally detected sacrococcygeal teratoma (SCT), which resulted in one caregiver suggesting termination of the pregnancy. This case demonstrates the importance of carefully considering the differential diagnosis of fetal abdomino-perineal masses when counseling parents. Copyright © 2006 John Wiley & Sons, Ltd.     

Human appropriation of net primary production (HANPP) in Nova Scotia,Canada

Photosynthetically fixed energy from the sun, in the form of net primary production, ultimately supports the majority of life on earth. Given the importance of this energy source, we calculate the human appropriation of net primary production (HANPP) for the province of Nova Scotia, Canada. We find that over 25% of potentially available production is appropriated by humans through harvest (forestry and agriculture) and land cover change. The level of appropriation in Nova Scotia is close to the global average, when methodological differences between studies are taken into account, but substantially less than in Austria and India where detailed surveys have also been conducted. Furthermore, HANPP is not distributed evenly throughout the province, but is instead concentrated in the north-central counties, where appropriation reaches 50%. We discuss the implications of these results, and the novel method used to obtain them, in the context of biophysical assessment and the species-energy hypothesis.     

Changing Species Richness and Composition in Canadian National Parks

Abstract: Canada's national parks and their surrounding areas differ markedly in size, climate, vegetation, and extent of human development. We tested the extent to which total species richness, native species richness, and the number of extirpations and introductions of terrestrial vertebrates were correlated with each of these factors. To do this, we used surveys of park fauna from the present and from the time of park establishment. Richness, extirpations, and introductions were all strongly related to climate. After we controlled for climate, smaller parks had higher rates of species loss than larger parks. Land-use patterns (forest cover and fragmentation, roads, etc.) within parks were strongly correlated with land use in the regions surrounding the parks, showing that parks have not been isolated from regional development. Richness and extirpations within parks were generally more strongly related to regional characteristics than to the characteristics of the parks themselves. Species richness and numbers of introduced species were higher in parks found in landscapes with greater fragmentation. Frequencies of extirpations were less clearly related to human-influenced habitat characteristics. Introductions and extinctions most often involved game species or species directly associated with human activities. There is little evidence of subtle ecological effects being responsible for species loss. Our results suggest that management should focus on direct human interventions, such as hunting, introduction of game species, and habitat fragmentation, in parks and surrounding areas.     

Hedonic housing prices and the demand for clean air

This paper investigates the methodological problems associated with the use of housing market data to measure the willingness to pay for clean air. With the use of a hedonic housing price model and data for the Boston metropolitan area, quantitative estimates of the willingness to pay for air quality improvements are generated. Marginal air pollution damages (as revealed in the housing market) are found to increase with the level of air pollution and with household income. The results are relatively sensitive to the specification of the hedonic housing price equation, but insensitive to the specification of the air quality demand equation.