Amniotic fluid-AFP in Down syndrome and other chromosome abnormalities

80·2 Per cent of 111 Down syndrome pregnancies had amniotic fluid (AF) alpha fetoprotein (AFP) levels on or below the median and 10·8 per cent at or below 0·5 MoM compared with 41·9 and 1·4 per cent of controls. These differences were even more striking when the gestational age was < 18 weeks compared with ⩾ 18 weeks. No such association was seen for other chromosome abnormalities including trisomy 18,45,X and mosaics, 47,XXY, 47,XXX, and other structural abnormalities and triploidy, even when high levels due to defects such as omphalocele and cystic hygroma were excluded. All cases of trisomy 13 and 80 per cent with 47,XYY had AF-AFP levels above the median. Selection of cases for karyotyping by a low level of AF-AFP would clearly fail to detect aneuploidies other than Down syndrome and is not recommended. A possible weak association between low maternal serum (MS) and AF-AFPs in Down syndrome was most evident at < 18 weeks, suggesting that MS screening between 16 and 18 weeks may be the most informative time.     

Biodiversity of microarthropods in agricultural soils: relations to processes

Soil microarthropods (principally mites and collembolans) are among the unseen faunal diversity in nearly all agricultural soils. Microarthropods participate in the complex food webs of soils, but their importance is seldom appreciated. Laboratory and field results show that microarthropods have impacts on organic debris, microbial decomposers, nematodes, roots and pathogenic fungi. However, their impact on primary production is only indirect. Opportunities for managing soil microarthropods in agricultural soils have been ignored.     

Hydrophobicity of soil colloids and heavy metal mobilization: effects of drying

Drying of soil may increase the hydrophobicity of soil and affect the mobilization of colloids after re-wetting. Results of previous research suggest that colloid hydrophobicity is an important parameter in controlling the retention of colloids and colloid-associated substances in soils. We tested the hypothesis that air-drying of soil samples increases the hydrophobicity of water-dispersible colloids and whether air-drying affects the mobilization of colloid-associated heavy metals. We performed batch experiments with field-moist and air-dried (25 degrees C) soils from a former sewage farm (sandy loam), a municipal park (loamy sand), and a shooting range site (loamy sand with 25% C(org)). The filtered suspensions (<1.2 microm) were analyzed for concentrations of dissolved and colloidal organic C and heavy metals (Cu, Cd, Pb, Zn), average colloid size, zeta potential, and turbidity. The hydrophobicity of colloids was determined by their partitioning between a hydrophobic solid and a hydrophilic aqueous phase. Drying increased hydrophobicity of the solid phase but did not affect the hydrophobicity of the dispersed colloids. Drying decreased the amount of mobilized mineral and (organo-)mineral colloids in the sewage farm soils but increased the mobilization of organic colloids in the C-rich shooting range soil. Dried samples released less colloid-bound Cd and Zn than field-moist samples. Drying-induced mobilization of dissolved organic C caused a redistribution of Cu from the colloidal to the dissolved phase. We conclude that drying-induced colloid mobilization is not caused by a change in the physicochemical properties of the colloids. Therefore, it is likely that the mobilization of colloids in the field is caused by increasing shear forces or the disintegration of aggregates.     

Longer-duration uses of tetracyclines and penicillins in U.S. food-producing animals: Indications and microbiologic effects

We review and analyze regulatory categories for longer duration of use (defined as ≥ 7 day) tetracyclines (TCs) and penicillins (PNs) approved for U.S. livestock and poultry, together with scientific studies, surveillance programs and risk assessments pertaining to antimicrobial resistance. Indications listed on a government database were grouped into three broad categories according to the terminology used to describe their use: disease control (C), treatment (T) and growth improvement (G). Consistent with mostly therapeutic uses, the majority (86%) of listed indications had C and/or T terms. Several studies showed interruption of early disease stages in animals and modulation of intestinal microflora. Longer-duration exposures are consistent with bacteriostatic modes of action, where adequate exposure time as well as concentration is needed for sufficient antimicrobial activity. Other effects identified included reduced animal pathogen prevalence, toxin formation, inflammation, environmental impacts, improved animal health, reproductive measures, nutrient utilization, and others. Several animal studies have shown a limited, dose-proportionate, selective increase in resistance prevalence among commensal animal bacteria following longer-duration exposures. Pathogen surveillance programs showed overall stable or declining resistance trends among sentinel bacteria. Quantitative, microbiologically detailed resistance risk assessments indicate small probabilities of human treatment failure due to resistance under current conditions. Evaluations of longer-duration uses of TCs, PNs, and other antimicrobial classes used in food-producing animals should consider mechanisms of activity, known individual- and population-level health and waste reduction effects in addition to resistance risks.