Tegan Darch - Academia.edu (original) (raw)

Papers by Tegan Darch

Environmental science & technology, Jan 25, 2016

The mobility and resupply of inorganic phosphorus (P) from the solid phase were studied in 32 soi... more The mobility and resupply of inorganic phosphorus (P) from the solid phase were studied in 32 soils from the UK. The combined use of diffusive gradients in thin films (DGT), diffusive equilibration in thin films (DET) and the 'DGT-induced fluxes in sediments' model (DIFS) were adapted to explore the basic principles of solid-to-solution P desorption kinetics in previously unattainable detail. On average across soil types, the response time (Tc) was 3.6 h, the desorption rate constant (k-1) was 0.0046 h-1, and the desorption rate was 4.71 nmol l-1 s-1. While the relative DGT-induced inorganic P flux responses in the first hour is mainly a function of soil water retention and % Corg, at longer times it is a function of the P resupply from the soil solid phase. Desorption rates and resupply from solid phase were fundamentally influenced by P status as reflected by their high correlation with P concentration in FeO strips, Olsen, NaOH-EDTA and water extracts. Soil pH and particl...

The American Journal of Clinical Nutrition, Oct 1, 2007

Background: Malnutrition in late infancy in developing countries may result from poor-quality com... more Background: Malnutrition in late infancy in developing countries may result from poor-quality complementary foods that displace breast milk. Objective: The objective of the study was to assess the effects of fortified complementary blends of different energy densities on growth, hemoglobin concentrations, and breast milk intake of 9-moold Zambian infants. Design: Infants were randomly assigned at 6 mo of age to receive for 3 mo a fortified blend of maize, beans, bambaranuts, and groundnuts [Chilenje Baby Mix (CBM); energy density: 68 kcal/100 g; n ҃ 37] or a similar blend with ␣-amylase (CBMA; energy density: 106 kcal/100 g; n ҃ 44). Cross-sectional data were obtained at 9 mo for a control group of infants (n ҃ 69) not given the diets. Breast milk intake was measured by using the dose-to-the-mother deuterium dilution technique. Results: No differences in weight or length z scores, all of which were within normal ranges, were seen between groups at 9 mo. Percentage fat mass was significantly (P ҃ 0.01) greater in the infants in both the CBM (23.2 Ȁ 2.7%) and CBMA (23.4 Ȁ 2.5%) groups than in the control group (21.6 Ȁ 2.6%). Hemoglobin concentrations were significantly (P ҃ 0.03) greater in both intervention groups (CBM group: 104 Ȁ 12 g/L: CBMA group: 103 Ȁ 12 g/L) than in the control group (98 Ȁ 14 g/L). Breast milk intake was not significantly (P ҃ 0.87) different between groups (CBM group: 614 Ȁ 271 g/d; CBMA group: 635 Ȁ 193 g/d; control group: 653 Ȁ 221 g/d).

European journal of clinical nutrition, 2015

Whether fat-free mass (FFM) and its components are depleted in eating-disorder (ED) patients is u... more Whether fat-free mass (FFM) and its components are depleted in eating-disorder (ED) patients is uncertain. Dual energy X-ray absorptiometry (DXA) is widely used to assess body composition in pediatric ED patients; however, its accuracy in underweight populations remains unknown. We aimed (1) to assess body composition of young females with ED involving substantial weight loss, relative to healthy controls using the four-component (4C) model, and (2) to explore the validity of DXA body composition assessment in ED patients. Body composition of 13 females with ED and 117 controls, aged 10-18 years, was investigated using the 4C model. Accuracy of DXA for estimation of FFM and fat mass (FM) was tested using the approach of Bland and Altman. Adjusting for age, height and pubertal stage, ED patients had significantly lower whole-body FM, FFM, protein mass (PM) and mineral mass (MM) compared with controls. Trunk and limb FM and limb lean soft tissue were significantly lower in ED patients...

International journal of obesity (2005), 2011

Low-birth weight has been proposed to programme central adiposity in childhood. However, there is... more Low-birth weight has been proposed to programme central adiposity in childhood. However, there is little information on associations between fetal weight gain and fat distribution within obese individuals. To investigate associations between birth weight and postnatal weight gain with body composition in a sample of obese children and adolescents. Body composition was measured using anthropometry, dual-emission X-ray absorptiometry and the 4-component model in 45 male and 76 female obese individuals aged 5-22 years. General linear models were used to investigate associations between birth weight standard deviation score (SDS), or change in weight SDS between birth and follow-up, and body composition, adjusting for age, pubertal status, height and gender. Birth weight SDS ranged from -1.86 to 3.46, and was inversely associated with current weight SDS after adjustment for height SDS. Birth weight SDS was weakly associated with waist and hip girths, but not waist-hip ratio or trunk fat...

International journal of obesity (2005), 2010

Body composition is increasingly measured in pediatric obese patients. Although dual-energy X-ray... more Body composition is increasingly measured in pediatric obese patients. Although dual-energy X-ray absorptiometry (DXA) is widely available, and is precise, its accuracy for body composition assessment in obese children remains untested. We aimed to evaluate DXA against the four-component (4C) model in obese children and adolescents in both cross-sectional and longitudinal contexts. Body composition was measured by DXA (Lunar Prodigy) and the 4C model in 174 obese individuals aged 5-21 years, of whom 66 had a second measurement within 1.4 years. The Bland-Altman method was used to assess agreement between techniques for baseline body composition and change therein. A significant minority of individuals (n=21) could not be scanned successfully due to their large size. At baseline, in 153 individuals with complete data, DXA significantly overestimated fat mass (FM; Delta=0.9, s.d. 2.1 kg, P<0.0001) and underestimated lean mass (LM; Delta=-1.0, s.d. 2.1 kg, P<0.0001). Multiple reg...

The American journal of clinical nutrition, 2007

Malnutrition in late infancy in developing countries may result from poor-quality complementary f... more Malnutrition in late infancy in developing countries may result from poor-quality complementary foods that displace breast milk. The objective of the study was to assess the effects of fortified complementary blends of different energy densities on growth, hemoglobin concentrations, and breast milk intake of 9-mo-old Zambian infants. Infants were randomly assigned at 6 mo of age to receive for 3 mo a fortified blend of maize, beans, bambaranuts, and groundnuts [Chilenje Baby Mix (CBM); energy density: 68 kcal/100 g; n = 37] or a similar blend with alpha-amylase (CBMA; energy density: 106 kcal/100 g; n = 44). Cross-sectional data were obtained at 9 mo for a control group of infants (n = 69) not given the diets. Breast milk intake was measured by using the dose-to-the-mother deuterium dilution technique. No differences in weight or length z scores, all of which were within normal ranges, were seen between groups at 9 mo. Percentage fat mass was significantly (P = 0.01) greater in the ...

Rapid Communications in Mass Spectrometry, 2008

Deuterium (2H) in water and urine can be measured by off-line and, more recently, on-line techniq... more Deuterium (2H) in water and urine can be measured by off-line and, more recently, on-line techniques using isotope ratio mass spectrometry (IRMS). We describe a new simple on-line pyrolysis method for the analysis of 2H/1H in water and urine samples by continuous flow IRMS, normally used for 2H/1H measurements in organic compounds. A deactivated column connected the split injector to a high-temperature conversion reactor (TC HD), and 0.5 microL of sample was injected. Accuracy and precision were determined with Vienna Standard Mean Ocean Water (VSMOW), Standard Light Antarctic Precipitation (SLAP), and Greenland Ice Sheet Precipitation (GISP). The range of linearity was measured with a calibration curve of enriched water from 0 up to 0.1 atom percent excess (APE) (i.e. -72 up to 6323 delta per mil (deltaD per thousand)) with a precision of &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;5 per thousand and accuracy ranging between 1 and 55 per thousand. Blinded reanalysis of urine samples by an equilibration device (Gas Bench) and by a dedicated pyrolysis system (TC/EA) was performed and results compared by the Bland-Altman test. Enrichments ranged between 600 and 2400 per thousand deltaD(VSMOW) with a precision of +/-5 per thousand. Urine enrichments described by our method were strongly correlated with values obtained by Gas Bench and TC/EA (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). There was a significant memory effect that was reduced by injecting the sample 15 times and discarding the first 10 injections, together with accurate furnace conditioning and appropriate cleaning of the syringe. Data indicate that the method is accurate, and that it can be used for water and urine deuterium determination when a Gas Bench or TC/EA instrument is not available and the amount of sample is limited.

European Journal of Clinical Nutrition, 2011

Critical Reviews in Environmental Science and Technology, 2013

ABSTRACT Phosphorus is known to be an important contributor to eutrophication of aquatic systems,... more ABSTRACT Phosphorus is known to be an important contributor to eutrophication of aquatic systems,1 but the role of organic phosphorus is often overlooked. This review uses a meta-analysis approach to investigate inorganic and organic phosphorus in organic fertilizers, soils and waters, including the quantification of organic phosphorous forms such as monoesters, diesters, and inositol hexakisphosphate. Across these media, organic phosphorus comprised 22–46% of the total phosphorus (by mass of phosphorus). Bioavailable organic phosphorus appears to be more mobile than recalcitrant forms. Organic phosphorus may represent a significant risk for eutrophication, and the risk may vary according to the season, but conclusions are hampered by a lack of data.

American Journal of Clinical Nutrition, 2010

Hydrometry and densitometry are widely used to assess pediatric body composition due to their eas... more Hydrometry and densitometry are widely used to assess pediatric body composition due to their ease of application. The accuracy of these techniques depends on the validity of age- and sex-specific constant values for lean tissue hydration or density. Empirical data on these constants, and their variability between individuals, are lacking. The objectives were to measure lean tissue hydration and density in a large sample of children and adolescents and to derive prediction equations. Body composition was measured in 533 healthy individuals (91% white) aged 4-23 y by using the 4-component model. Age- and sex-specific median values for hydration and density were obtained by using the LMS (lambda, mu, sigma) method. Regression analysis was used to generate prediction equations on the basis of age, sex, and body mass index SD score (BMI SDS). Values were compared with those in previously published predictions. Age-associated changes in density and hydration differed between the sexes. Compared with our empirical values, use of published values resulted in a mean bias of 2.1% fat (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). Age, sex, and BMI SDS were all significant predictors of lean tissue hydration and density. With adjustment for age and sex, hydration was higher, and density lower, in higher-BMI SDS individuals. The chemical maturation of lean tissue is not a linear process and proceeds differently in males and females. Previously published reference values are inaccurate and induce clinically significant bias in percentage fat. New empirical reference values are provided for use in pediatric hydrometry and densitometry. Further research that extends to cover nonwhite ethnic groups is needed.

American Journal of Clinical Nutrition, 2012

A routine pediatric clinical assessment of body composition is increasingly recommended but has l... more A routine pediatric clinical assessment of body composition is increasingly recommended but has long been hampered by the following 2 factors: a lack of appropriate techniques and a lack of reference data with which to interpret individual measurements. Several techniques have become available, but reference data are needed. We aimed to provide body-composition reference data for use in clinical practice and research. Body composition was measured by using a gold standard 4-component model, along with various widely used reference and bedside methods, in a large, representative sample of British children aged from 4 to ≥20 y. Measurements were made of anthropometric variables (weight, height, 4 skinfold thicknesses, and waist girth), dual-energy X-ray absorptiometry, body density, bioelectrical impedance, and total body water, and 4-component fat and fat-free masses were calculated. Reference charts and SD scores (SDSs) were constructed for each outcome by using the lambda-mu-sigma method. The same outcomes were generated for the fat-free mass index and fat mass index. Body-composition growth charts and SDSs for 5-20 y were based on a final sample of 533 individuals. Correlations between SDSs by using different techniques were ≥0.68 for adiposity outcomes and ≥0.80 for fat-free mass outcomes. These comprehensive reference data for pediatric body composition can be used across a variety of techniques. Together with advances in measurement technologies, the data should greatly enhance the ability of clinicians to assess and monitor body composition in routine clinical practice and should facilitate the use of body-composition measurements in research studies.

Journal of Environment Quality, 2015

Phosphorus (P) contributes to eutrophication of surface waters and buffer strips may be implement... more Phosphorus (P) contributes to eutrophication of surface waters and buffer strips may be implemented to reduce its transfer from agricultural sources to watercourses. This study was conducted to test the hypothesis that soil type and slope influence the retention of dissolved organic P and inorganic orthophosphate in agricultural runoff in 2-m-wide buffer strip soils. A solution, comprised of dissolved orthophosphate and the organic P compounds glucose-1-phosphate, RNA, and inositol hexakisphosphate (1.8 mg L -1 total P) and a chloride tracer, was applied as simulated overland flow to grassland soil blocks (2 m long × 0.5 m wide × 0.35 m deep), containing intact clay or loam soils, at slope angles of 2, 5, and 10°. Phosphorus forms were determined in the surface and subsurface flow from the soil blocks. Slope had no significant effect on the hydrological behavior of the soil blocks or on the retention of any form of P at the water application rate tested. The clay soil retained 60% of the unreactive P and 21% of the reactive P applied. The loam soil retained 74% of the unreactive P applied but was a net source of reactive P (the load increased by 61%). This indicates leaching of native soil P or hydrolysis of organic compounds and complicates our understanding of P retention in buffer strip soils. Our results suggest that a 2-m buffer strip may be more effective for reducing dissolved unreactive P transfers to surface waters than for reducing the eutrophication risk posed by dissolved reactive P.