Impact of stereoacuity on simulated cataract surgery ability.

BACKGROUND AND OBJECTIVES: There exists a long-standing perception that diminished stereoacuity has a detrimental effect on microsurgical ability and skills acquisition. This has potential implications on the enrolment of surgical trainees into ophthalmology and other microsurgery specialities. However, strong evidence in this area is lacking. This case-control study aims to establish the exact level of stereopsis impairment at which a statistical drop in surgical performance occurs. METHODS: Fifty participants were enrolled from the University of Dundee Medical School and the NHS Tayside Foundation Doctor programme. Participants were assessed for their stereopsis level before completing an orientation module on an ophthalmic surgical simulator. They were then required to repeat a task four times. Automated and objective performance levels were recorded and analysed. RESULTS: Nineteen (38%) had stereopsis lower than the defined normal of 60 seconds of arc (arcsec). Statistical analysis found no correlation between visual acuity and surgical performance. No statistical difference was found between performance scores and stereoacuities of 30, 60 and 120 arcsec. A statistically significant difference was discovered in the surgical performance of participants with a stereoacuity worse than 120 arcsec (total score = -69.85) as compared to the ones with a stereoacuity of 120 arcsec or better (total score = -42.23) with p = 0.010. CONCLUSIONS: This study provides evidence of a specific level of stereopsis where statistical degradation of surgical performance occurs. The findings of this work may help formulate policy on stereoacuity standards required to commence microsurgical training.

Vision screening in children: a retrospective study of social and demographic factors with regards to visual outcomes.

BACKGROUND: Amblyopia and its risk factors have been demonstrated to be more common among children from low socioeconomic backgrounds. We sought to investigate this association in a region with orthoptic-delivered screening and whole population coverage, and to also examine the association of the Health Plan Indicator (HPI) with screening outcome. METHODS: Screening examination outcomes, postcodes and HPIs were extracted from the community child health database for every child who underwent preschool vision screening between March 2010 and February 2011 Tayside. We obtained the Scottish Index of Multiple Deprivation score for every child as a measure of area-based deprivation. We assessed the vulnerability/needs of the individual family through the HPI-'Core' (children and families receiving universal health visiting service), 'Additional' (receiving additional health/social support) and 'Intensive' (receiving high levels of support). The outcomes from follow-up examinations for those who failed screening were extracted from the orthoptic department database. RESULTS: 4365 children were screened during the year 2010-2011 of whom 523 (11.9%) failed. The odds of children from the least deprived socioeconomic group passing the visual screening test was 1.4 times higher than those from the most deprived socioeconomic group (OR 1.4, 95% CI 1.07 to 1.89, p=0.01). The odds of a child from a family assigned as 'Intensive' failing the preschool visual screening test was three times greater than the odds of a child from a family assigned as 'Core' (OR 3.59, 95% CI 1.6 to 7.8, p=0.001). CONCLUSIONS: We found that children from the most deprived backgrounds and those from unstable homes were more likely to fail preschool vision screening.

Quality of life in children with primary antibody deficiency.

Primary antibody deficiency disorders (PADs) can have an excellent outlook if diagnosed early and treated appropriately, but require lifelong treatment with immunoglobulin replacement. Some carry risks of inflammatory complications even with optimal treatment. Quality of life (QoL) and the psychological impact of PADs has been relatively little studied, particularly in children. The purpose of this study was to evaluate QoL and psychological impact in a large group of children affected by a range of PADs, as well as a group with transient hypogammaglobulinemia of infancy (THI). Both parental and, where appropriate, child ratings, were collected using standardised questionnaires (PedsQL and SDQ). Higher rates of psychological difficulties, particularly emotional and peer-relationship difficulties were found in children with PAD when compared with healthy controls. Quality of life was poorer than in healthy controls, and also worse than in children affected by diabetes mellitus. Variations in QoL and the degree of psychological difficulties were found between specific diagnostic groups, with children affected by THI being amongst those with the lowest scores for QoL. Further studies are needed to corroborate and extend these findings, but this study confirms previous findings that primary antibody deficiency has a significant impact on quality of life and psychological well-being, and additionally suggests that the impact varies according to severity of the underlying condition. For those with significant difficulties psychological intervention at an early stage may be beneficial.

Circulating and placental endoglin concentrations in pregnancies complicated by intrauterine growth restriction and preeclampsia.

Inadequate trophoblast invasion and spiral artery remodeling leading to poor placental perfusion and hypoxia are believed to underlie preeclampsia (PE) and intrauterine growth restriction (IUGR). Recent studies implicate increased circulating endoglin as a contributor to the pathogenesis of PE. The objective of this study was to determine whether placental and circulating endoglin concentrations are altered in pregnancies complicated by intrauterine growth restricted (IUGR) infants and to address the role of hypoxia on the regulation of placental endoglin. We analyzed 10 placentas each from normal pregnant (NP), PE, and IUGR subjects. Endoglin levels were 2.5-fold higher in preeclamptic placentas compared to NP (15.4+/-2.6 versus 5.7+/-1.0, p<0.01). In contrast, endoglin levels were similar in NP and IUGR placentas (5.7+/-1.0 vs 5.9+/-1.1, p=NS). Placentas from pregnancies with both PE and IUGR exhibited endoglin levels comparable to the PE group and significantly different from normotensive pregnancies with and without IUGR pregnancies (mean 14.9+/-4.0, n=9, p=0.013). Soluble endoglin concentrations in maternal plasma were comparable in NP and IUGR, but higher in women with PE (n=10 per group, p<0.05). Despite a 2-fold increase in hypoxia inducible factor, HIF-1alpha, we did not observe endoglin upregulation in NP, PE, or IUGR placental villous explants exposed to hypoxia (2% oxygen). In contrast to PE, placental or circulating endoglin is not increased in normotensive women delivering small, asymmetrically grown (IUGR) infants at term. The placentas of women with IUGR appear to be fundamentally different from PE women with respect to endoglin, despite the proposed common pathology of deficient trophoblast invasion/spiral artery remodeling and poor placental perfusion.

Proteasomal activity in placentas from women with preeclampsia and intrauterine growth restriction: implications for expression of HIF-alpha proteins.

Hypoxia-inducible transcription factor-1alpha and -2alpha (HIF-alpha) proteins and regulated genes are increased in preeclamptic (PE) placentas. Although placental hypoxia likely stabilizes HIF-alpha proteins, we previously reported that there is also a defect in oxygen-dependent reduction of HIF-alpha proteins in PE relative to normal pregnant (NP) placentas that could contribute to their over-expression. After a 4-h exposure to 2% oxygen, placental villous explants were exposed to 21% oxygen over 90 min. As assessed by Western analysis, the defective oxygen-dependent reduction of HIF-1alpha protein in villous explants from PE placenta was unaffected by the protein synthesis inhibitor, cycloheximide. However, after incubation with the proteasomal inhibitor, clasto-lactacystin, oxygen-dependent reduction of HIF-1alpha protein was markedly and similarly impaired in the villous explants from both normal and PE placentas. Thus, impairment of protein degradation rather than increased synthesis causes inadequate oxygen-dependent reduction of HIF-1alpha protein in PE placentas. Immunoprecipitation studies revealed comparable association of HIF-1alpha with von Hippel Lindau (VHL) protein in placentas from NP and PE women. Furthermore, prolyl hydroxylase-3 protein was appropriately upregulated in the PE placentas as determined by Western analysis paralleling the increases of HIF-alpha proteins. These results suggest that molecular events leading to the formation of the HIF-1alpha:VHL:ubiquitin ligase complex are most likely not impaired in PE placentas. Finally, proteasomal trypsin, chymotrypsin, and peptidyl glutamyl-like activities were significantly reduced by approximately 1/3 in PE placentas by using specific peptide substrates coupled to a fluorescent tag. Unexpectedly, however, they were even further decreased in placentas from normotensive women delivering growth restricted babies >37 weeks gestation-placentas which do not have elevated HIF-alpha proteins. In conclusion, accumulation of HIF-alpha proteins in PE placentas may occur as a consequence of both increased formation secondary to relative ischemia/hypoxia and reduced degradation after reperfusion/oxygenation consequent to proteasomal dysfunction. In contrast, in placentas from normotensive women delivering growth restricted babies >37 weeks gestation, proteasomal activity, albeit markedly reduced, is adequate to cope with degradation of HIF-alpha proteins, which have not been increased by an hypoxic environment.

Mercury methylation by dissimilatory iron-reducing bacteria.

The Hg-methylating ability of dissimilatory iron-reducing bacteria in the genera Geobacter, Desulfuromonas, and Shewanella was examined. All of the Geobacter and Desulfuromonas strains tested methylated mercury while reducing Fe(III), nitrate, or fumarate. In contrast, none of the Shewanella strains produced methylmercury at higher levels than abiotic controls under similar culture conditions. Geobacter and Desulfuromonas are closely related to known Hg-methylating sulfate-reducing bacteria within the Deltaproteobacteria.

Microscopy and culture for Trichomonas vaginalis: are both required?

Many genitourinary medicine clinics have stopped routinely performing both wet preparation microscopy and cultures to diagnose Trichomonas vaginalis (TV). Our directorate stopped microscopy when screening asymptomatic women. This audit considers whether both tests continue to be warranted for symptomatic female patients. The discrepancy between microscopy and culture results leads us to recommend that both remain necessary. Sampling standardization and improved documentation are discussed.

The influence of sulfide on solid-phase mercury bioavailability for methylation by pure cultures of Desulfobulbus propionicus (1pr3).

To help understand the mechanism and control of Hg uptake in Hg-methylating bacteria, we investigated the effect of sulfide on Hg methylation by pure cultures of the sulfate-reducing bacterium Desulfobulbus propionicus (1pr3). Our previous research in natural sediments has suggested that Hg methylation occurs most rapidly when sulfide concentrations favor formation of neutral dissolved Hg-S species. In this study, the chemical speciation of Hg in culture media was manipulated by growing D. propionicus across a range of sulfide concentrations, with inorganic Hg (HgI) added in the form of ground ores. A solid-phase, rather than a dissolved source of Hg, was used to simulate the controls on Hg partitioning between solid and aqueous phases found in natural sediments. Methylmercury (MeHg) production by cultures was not related to the absolute solid-phase concentration of Hg in the ores, and it was only weakly related to the dissolved HgI concentration in the medium. However, MeHg production was linearly related to the calculated concentration of the dominant neutral complex in solution, HgS degrees. Furthermore, the diffusive membrane permeability of HgS degrees, as estimated from its octanol-water partitioning coefficient, was found to be sufficient to support MeHg production by cells. The present paper expands on our previous work by providing experimental support of our hypothesis that sulfide influences methylation by affecting the speciation of dissolved HgI and its uptake via passive diffusion.

Aspects of bioavailability of mercury for methylation in pure cultures of Desulfobulbus propionicus (1pr3).

We have previously hypothesized that sulfide inhibits Hg methylation by decreasing its bioavailability to sulfate-reducing bacteria (SRB), the important methylators of Hg in natural sediments. With a view to designing a bioassay to test this hypothesis, we investigated a number of aspects of Hg methylation by the SRB Desulfobulbus propionicus, including (i) the relationship between cell density and methylmercury (MeHg) production, (ii) the time course of Hg methylation relative to growth stage, (iii) changes in the bioavailability of an added inorganic Hg (Hg(I)) spike over time, and (iv) the dependence of methylation on the concentration of dissolved Hg(I) present in the culture. We then tested the effect of sulfide on MeHg production by this microorganism. These experiments demonstrated that under conditions of equal bioavailability, per-cell MeHg production was constant through log-phase culture growth. However, the methylation rate of a new Hg spike dramatically decreased after the first 5 h. This result was seen whether methylation rate was expressed as a fraction of the total added Hg or the filtered Hg(I) concentration, which suggests that Hg bioavailability decreased through both changes in Hg complexation and formation of solid phases. At low sulfide concentration, MeHg production was linearly related to the concentration of filtered Hg(I). The methylation of filtered Hg(I) decreased about fourfold as sulfide concentration was increased from 10(-6) to 10(-3) M. This decline is consistent with a decrease in the bioavailability of Hg(I), possibly due to a decline in the dissolved neutral complex, HgS(0).

A survey of size-specific mercury concentrations in game fish from Maryland fresh and estuarine waters.

A survey of size-specific mercury (Hg) concentrations in game fish from a subset of Maryland fresh and estuarine waters was conducted, in which Hg concentrations in 112 fish from seven freshwater impoundments and three tidal and four estuarine locations in Chesapeake Bay and its tributaries were measured. Striped bass (Morone saxatilis) was the most intensively examined species. Of the fish examined, the largest freshwater sportfish contained the highest Hg concentrations. Striped bass and largemouth bass (Micropterus salmoides) from Chesapeake Bay and its tributaries contained less Hg at the same size than the same species in fresh waters. Large striped bass, chain pickerel (Esox niger), and walleye (Stizostedion vitreum) from Deep Creek Lake and Liberty Reservoir exceeded the FDA action level of 1 mg Hg/kg. Striped bass, largemouth bass, and white crappie (Pomoxis annularis) in other impoundments equaled or exceeded a common advisory level of 0.5 mg Hg/kg. Large differences in size-normalized Hg concentrations among lakes and particularly between fresh and salt waters highlight the large differences in MeHg production and bioaccumulation among ecosystems. This work indicates that a more comprehensive study of Hg in Maryland fish is warranted to protect human and wildlife health.

Increased umbilical cellular fibronectin concentrations are associated with a decreased prevalence of growth restriction in preeclampsia.

OBJECTIVE: Cellular fibronectin (cFN), a marker of endothelial activation, is elevated in maternal and cord blood in preeclampsia. We tested whether maternal or fetal cFN is related to fetal growth restriction in preeclampsia, in the context of gestational age at delivery. METHODS: Cellular fibronectin was measured in maternal and cord blood of 29 preeclamptic women and their infants delivered at Magee-Womens Hospital at 25-41 weeks of gestation. Relationships among maternal and cord cFN, birth weight, birth weight percentile, and ponderal index were evaluated using Pearson correlation and regression analyses controlled for gestational age. RESULTS: Cord cFN was not significantly related to maternal cFN (r = -.34, P = .08) or gestational age (r = -.32, P = .09). The relationship of maternal cFN to each index of infant size was not significant. By contrast, higher cord cFN predicted higher birth weight, birth weight percentile, and ponderal index (P < .05). CONCLUSION: Elevated maternal and cord cFN concentrations have been reported in pregnancy complicated by preeclampsia. This study assessed the relationship among maternal cFN, cord cFN, and indices of fetal growth in preeclampsia. Elevated cord cFN was associated with measures of better fetal growth.

Effect of pulsed dexamethasone therapy on tolerance of intravenously administered lipids in extremely low birth weight infants.

We investigated the effect of dexamethasone on parenteral lipid tolerance in 7-day-old extremely low birth weight infants (n = 28) in a randomized, double-blind trial. Serum triglycerides were measured before and after 3 days of dexamethasone or placebo treatment. Infants treated with dexamethasone responded with higher triglyceride concentrations and greater sensitivity to incremental increases in the intravenous lipid dose.

Post-traumatic stress disorder in children and adolescents following road traffic accidents.

BACKGROUND: Post-traumatic stress disorder (PTSD) can be a persistent and disabling psychiatric disorder. There is little systematic research into the psychiatric consequences of road traffic accidents (RTAs) in children and adolescents. METHOD: A consecutive sample of 8-16-year-olds attending an accident and emergency department following RTAs were screened for PTSD. Potential cases and their parent(s) were interviewed with semi-structured research instruments about six weeks and six months after the accident. RESULTS: Fifty-three (45%) of the 119 subjects fell above PTSD cut-off on the Frederick's Reaction Index. Thirty-three (75%) of the 44 cases met DSM-IV criteria for PTSD. In half of these other psychiatric disorders were present, including major depressive disorder and anxiety disorders. Being female, involvement in car accidents and pre-existing depression and anxiety were associated with developing PTSD. Seventeen per cent of the sample continued to be symptomatic six months after the accident. CONCLUSIONS: PTSD is a common consequence of RTAs. Liaison with accident and emergency departments would enhance the early detection and follow-up of children at risk of developing PTSD.

Evidence of endothelial activation and endothelial activators in cord blood of infants of preeclamptic women.

OBJECTIVE: In preeclampsia markers of endothelial activation (e.g., increased cellular fibronectin and activities that alter in vitro endothelial function (e.g., stimulation of nitric oxide and prostacyclin generation) are increased in the maternal circulation. We tested preeclamptic infant blood for these markers and activities and correlated these findings with fetal growth. STUDY DESIGN: Plasma was obtained from 17 term nulliparcus preeclamptic and normal pregnant women and their infants and from 8 additional preeclamptic mother-baby pairs from earlier gestations. Plasma cellular fibronectin and production of nitric oxide and prostacyclin by cultured endothelial cells exposed to 2% plasma were measured. RESULTS: Cellular fibronectin was higher in maternal plasma of preeclamptic than nonpregnant women (6.1 +/- 0.29 vs 4.2 +/- 0.27 microgram/ml, p < 0.01), as were stimulated endothelial nitric oxide and prostacyclin production (nitric oxide 42.5 +/- 3.9 vs 26.9 +/- 2.3 nmol nitrite/microgram protein/24 hours, p < 0.05; prostacyclin 261.7 +/- 31.2 vs 151.9 +/- 18.7 pg prostaglandin F1 alpha/microgram protein/24 hours, p < 0.05). In the preeclamptic infants cellular fibronectin was also greater (3.3 +/- 0.15 vs 2.6 +/- 0.14 microgram/ml, p < 0.01), as was endothelial nitric oxide production in response to the plasma (24.4 +/- 1.1 vs 21.4 +/- 0.09 mumol/L nmol nitrite/microgram protein/24 hours, p < 0.05). Prostacyclin production was not significantly different. In preeclamptic infants across a wide gestational age there was no correlation of endothelial activation and fetal growth. CONCLUSIONS: Infants of women with preeclampsia may be affected by endothelial dysfunction, as well as reduced uteroplacental perfusion.

Pulse dexamethasone does not impair growth and body composition of very low birth weight infants.

OBJECTIVE: Evaluation of repeated pulses of dexamethasone (PDEX), given to improve cardiopulmonary outcome, on growth of very low birth weight (VLBW, < 1500 g) infants. METHODS: In this prospective, double-blind, randomized clinical trial, VLBW infants mechanically ventilated at 1 week of age received intravenous PDEX or saline placebo (P) for 3 days, every 10 days, until no supplemental oxygen or ventilation was required or 36 weeks postmenstrual age (PMA). Weight gain, fluid intake, caloric intake, and serum glucose were monitored throughout the study. Nutritional assessment at 36 weeks PMA consisted of weight, length, head circumference, skinfold thickness measures, body composition by total body electrical conductance, and bone mineral content (BMC) by single beam photon absorptiometry. RESULTS: 37 PDEX and 31 P infants survived at least 36 days and completed the protocol. Average daily weight gain, fluid intake and caloric intake were not different between groups. The pattern of weight gain (g/kg/day, mean +/- SD) was different: PDEX infants showed significant growth delay during (3.0 +/- 11.4) and immediately after (7.8 +/- 8.7) each pulse, with subsequent growth acceleration (18.3 +/- 8.2) until the next steroid pulse. In contrast, growth rate of P infants was constant (12.6 +/- 3.7) (p = 0.04). Hyperglycemia requiring insulin therapy occurred only in the PDEX group (10/37). The catch-up growth noted between pulses in the PDEX group was explained only in part by insulin therapy. At 36 weeks PMA, there were no differences between groups in body size, composition, or BMC. CONCLUSION: PDEX negatively affected glucose metabolism and growth patterns during and immediately after drug exposure. However, assessment near term gestational age showed similar body composition and size in both groups.

Effect of pulse dexamethasone therapy on the incidence and severity of chronic lung disease in the very low birth weight infant.

We conducted a prospective, randomized, double-blind trial to assess the efficacy and safety of pulse doses of dexamethasone on survival without supplemental oxygen in very low birth weight infants at high risk of having chronic lung disease. Seventy-eight infants with birth weights < or = 1500 gm who were ventilator dependent at 7 days of postnatal age were randomly assigned to receive pulse doses of dexamethasone, 0.5 mg/kg per day, divided twice daily (n = 39), or an equivalent volume of saline solution placebo (n = 39), for 3 days at 10-day intervals until they no longer required supplemental oxygen or assisted ventilation, or reached 36 weeks of postmenstrual age. At study entry, the groups did not differ by birth weight, gestational age, or severity of lung disease. At 36 weeks of postmenstrual age, there was both a significant increase in survival rates without oxygen supplementation (p = 0.03) and a significant decrease in the incidence of chronic lung disease (p = 0.047) in the group that received pulse therapy. Supplemental oxygen requirements were less throughout the study period in the group that received repeated pulse doses of dexamethasone (p = 0.013). The total numbers of deaths and the durations of supplemental oxygen, ventilator support, and hospital stay did not differ between groups. Recorded side effects in the pulse therapy group were minimal and included an increase in the use of insulin therapy for hyperglycemia (p < 0.05). We conclude that in this population of very low birth weight infants, treatment with pulse doses of dexamethasone resulted in improvement in pulmonary outcome without clinically significant side effects.

Accumulation of selenium in a model freshwater microbial food web.

The transfer of selenium between bacteria and the ciliated protozoan, Paramecium putrinum, was examined in laboratory cultures. The population growth of the ciliate was not inhibited in the presence of the highest concentrations of dissolved selenite or selenate tested (10(3) micrograms liter-1). Experiments with radioactive 75selenite or 75selenate indicated that accumulation of selenium by ciliates through time was low when feeding and metabolism were reduced by incubating at 0 degrees C. However, selenium accumulated in ciliate biomass during incubation with dissolved 75Se and bacteria at 24 degrees C and also when bacteria prelabeled with 75Se were offered as food in the absence of dissolved selenium. When 75Se-labeled bacterial food was diluted by the addition of nonradioactive bacteria, the amount of selenite and selenate in ciliates decreased over time, indicating depuration by the ciliates. In longer-term (> 5-day) fed-batch incubations with 75selenite-labeled bacteria, the selenium concentration in ciliates equilibrated at approximately 1.4 micrograms of Se g (dry weight)-1. The selenium content of ciliates was similar to that of their bacterial food on a dry-weight basis. These data indicate that selenium uptake by this ciliate occurred primarily during feeding and that biomagnification of selenium did not occur in this simple food chain.

Characterization of a new thermophilic sulfate-reducing bacterium Thermodesulfovibrio yellowstonii, gen. nov. and sp. nov.: its phylogenetic relationship to Thermodesulfobacterium commune and their origins deep within the bacterial domain.

A thermophilic sulfate-reducing vibrio isolated from thermal vent water in Yellowstone Lake, Wyoming, USA is described. The gram-negative, curved rod-shaped cells averaged 0.3 micrometer wide and 1.5 micrometers long. They were motile by means of a single polar flagellum. Growth was observed between 40 degrees and 70 degrees C with optimal growth at 65 degrees C. Cultures remained viable for one year at 27 degrees C although spore-formation was not observed. Sulfate, thiosulfate and sulfite were used as electron acceptors. Sulfur, fumarate and nitrate were not reduced. In the presence of sulfate, growth was observed only with lactate, pyruvate, hydrogen plus acetate, or formate plus acetate. Pyruvate was the only compound observed to support fermentative growth. Pyruvate and lactate were oxidized to acetate. Desulfofuscidin and c-type cytochromes were present. The G + C content was 29.5 mol%. The divergence in the 16 S ribosomal RNA sequences between the new isolate and Thermodesulfobacterium commune suggests that these two thermophilic sulfate-reducing bacteria represent different genera. These two bacteria depict a lineage that branches deeply within the Bacteria domain and which is clearly distinct from previously defined phylogenetic lines of sulfate-reducing bacteria. Strain YP87 is described as the type strain of the new genus and species Thermodesulfovibrio yellowstonii.

Mercury methylation in aquatic systems affected by acid deposition.

Recently, it has been noted that fish in acidified lakes may contain elevated levels of mercury. While there is correlation among lakes between depressed pH and high mercury concentrations in fish, the cause of this problem is unknown. A number of hypotheses have been advanced in explanation, including increased mercury deposition, changes in mercury mobility due to acidification, pH dependent changes in mercury uptake by biota, and alterations in population size and/or structure which result in increased bioaccumulation in fish. Because fish accumulate mercury mainly in an organic form, methylmercury, changes in the biogeochemical cycling of this compound might account for elevated bioaccumulation. Mercury methylation is predominantly a microbial process which occurs in situ in lakes. This review focuses on microbiological and biogeochemical changes that may lead to increased levels of methylmercury in fresh waters impacted by acid-deposition. In particular, we focus on the hypothesis that sulfate-reducing bacteria are important mediators of metal methylation in aquatic systems and, moreover, that sulfate-deposition may stimulate methylmercury production by enhancing the activity of sulfate-reducing bacteria in sediments.