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PubMed1994

[Progression of coronary sclerosis after smoking cessation].

Cigarette smoking is an established risk factor for the development of coronary artery disease, but whether cessation of heavy smoking influences progression of coronary artery disease is unclear. In 390 patients (359 men, 31 women; 52.4 +/- 6.7 SD years) with coronary artery disease, two coronary angiograms were performed at an interval of 62.4 +/- 23.5 months. Smoking habits were obtained by questionnaires. Progression of coronary artery disease was defined as the sum of new stenoses, progression of existing stenoses and new coronary occlusions. Multivariate classification analyses of risk factor profile revealed cigarette smoking (amount per day and length of time) as the most relevant factor for progression of coronary artery disease. Non-smokers had a progression score of 0.96 (95% confidence interval: 0.63-1.28) over the observation period. Former smokers (20.2 +/- 11.8 cigarettes/day for 19.4 +/- 7.6 years) who quit about 10 years before the first angiogram showed a progression of 2.20 (95% confidence interval: 1.77-2.63; p < 0.01) compared to non-smokers. Those smokers (23.8 +/- 9.2 cigarettes/day for 31.3 +/- 7.0 years) who quit at the time of the first angiogram showed a progression of 2.47 (95% confidence interval: 1.97-2.97; p < 0.001). Current smokers (20.5 +/- 9.7 cigarettes/day for 34.8 +/- 8.5 years) had a progression of 3.17 (95% confidence interval: 2.35-3.99; p < 0.001). The data indicate that former heavy cigarette smoking continues to act as a significant risk factor for progression of coronary artery disease even after cessation. This does not mean that current cigarette smokers should not stop.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2003

Accelerated degradation of methyl iodide by agrochemicals.

The fumigant methyl iodide (MeI, iodomethane) is considered a promising alternative to methyl bromide (MeBr) for soil-borne pest control in high-cash-value crops. However, the high vapor pressure of MeI results in emissions of a significant proportion of the applied mass into the ambient air, and this may lead to pollution of the environment. Integrating the application of certain agrochemicals with soil fumigation provides a novel approach to reduce excessive fumigant emissions. This study investigated the potential for several agrochemicals that are commonly used in farming operations, including fertilizers and nitrification inhibitors, to transform MeI in aqueous solution. The pseudo-first-order hydrolysis half-life (t(1/2)) of MeI was approximately 108 d, while the transformation of MeI in aqueous solutions containing selected agrochemicals was more rapid, with t(1/2) < 100 d (t(1/2) < 0.5 d in some solutions containing nitrification inhibitors). The influence of these agrochemicals on the rate of MeI degradation in soil was also determined. Adsorption to soil apparently reduced the availability of some nitrification inhibitors in the soil aqueous phase and lowered the degradation rate in soil. In contrast, addition of the nitrification inhibitors thiourea and allylthiourea to soil significantly accelerated the degradation of MeI, possibly due to soil surface catalysis. The t(1/2) of MeI was <20 h in thiourea- and allylthiourea-amended soil, considerably less than that in unamended soil (t(1/2) > 300 h).

Adsorption↗
PubMed1999

Optimal operating parameters in the composting of swine manure with wastepaper.

A series of experiments were conducted to determine the optimal conditions for composting of swine manure and wastepaper. The aeration rate and mixing ratio were the variables investigated. In the first study (Study-1), four experiments each with the same mixing ratio but a different aeration rate were carried out. In the second study (Study-2), different mixing ratios were investigated, each however with the same aeration rate which was found to be optimal from Study-1. Composting efficiencies were evaluated on the temperature profile and the reduction of C/N ratio. From the aeration rates of 200, 500, 1000, and 1500 mL/min.kg_vs that were evaluated, the aeration rate of 500 mL/min.kg_vs and higher showed good results. In Study-2, where the initial C/N ratios were 20, 25, 30, and 35 respectively, the C/N ratio of 30 was found to be optimal. In conclusion, the composting of swine manure with the amendment of wastepaper was best carried out at the aeration of > 500 mL/min.kg_vs and C/N ratio of 30.

Air↗
PubMedDate not supplied

Compost and calcium surface treatment effects on subsoil chemistry in acidic minespoil columns.

Surface incorporation of a liming agent in combination with compost or biosolids is a proven way to revegetate acidic minespoils, but little is known about the effect of the surface amendments on subsoil chemistry. We conducted a greenhouse column experiment to investigate how different surface amendments affected plant growth and subsoil chemistry in highly acidic minespoil material. Columns were filled with shale minespoil material (pH approximately 2.5), amended with CaCO3, CaSO4 x 2H2O (gypsum), and two rates of compost, and seeded with birdsfoot trefoil (Lotus corniculatus L.) and 'Kentucky 31' tall fescue (Festuca arundinacea Schreb.). We measured leachate and plant growth over a 170-d period with extensive irrigation. Without CaCO3, plants could only grow at the high compost rate (68.8 g kg(-1)), even though the soil pH in those treatments was below 3.5, indicating the capability of natural organic matter to detoxify Al(3+) by forming Al-organic matter complexes. Compost had no effect on the subsoil. When CaCO3 or gypsum was added to the surface, extractable Ca increased in the subsoil, but there was no relevant increase in subsoil pH. Even in the first 5 cm of subsoil material, extractable Al did not decrease very much, possibly because a jurbanite-like solid phase controlled subsoil Al(3+) activities. During the reclamation of highly acidic minespoil material one should therefore not expect significant effects of the surface treatment on the untreated subsoil. A sufficient root zone would have to be achieved by incorporating the liming agent down to the desired rooting depth.

Antacids↗
PubMed2001

Is success a sin? A conversation with the reverend Peter J. Gomes. Interview by David A. Light.

The difficult task of achieving worldly success while also storing up spiritual treasure is perennially with us, in good times and in bad. Today, however, as the economy has cooled and companies have demonstrated their mortality, questions about meaning and value appear more relevant, even urgent. HBR associate editor David A. Light recently spoke with the Reverend Peter J. Gomes, one of the nation's best-known preachers and the minister at Harvard University's Memorial Church, about why and how it is both possible and necessary to reconcile a life of success with a life of faith. To do so, says Gomes, you must first "get used to it"--come to terms with the age-old tension between being rich in spirit and rich in worldly goods. Second, you should "get over it"--arrive at an understanding of the value and responsibilities associated with power and wealth. Finally, "get on with it"--figure out how you can live your life spiritually while continuing to lead in the business world. For those wondering how to get on with spiritual development, Gomes cites the growing phenomenon of senior executives gathering with peers--out of shared need, not shared accomplishment--to pray, study sacred texts, and share their religious life together. He counsels that it's never too late to get on with it: We can amend life at any time, whether we're 35, 45, or 75. Gomes concludes that business will continue to be one of the most significant forces in American culture, but it will always struggle against people's need for a perspective that is beyond this world's.

Achievement↗
PubMed1998

Effect of calcium on the surfactant tolerance of a fluoranthene degrading bacterium.

Surfactants are known to increase the apparent aqueous solubility of polycyclic aromatic hydrocarbons (PAHs) and may thus be used to enhance the bioavailability and thereby to stimulate the biodegradation of these hydrophobic compounds. However, surfactants may in some cases reduce or inhibit biodegradation because of toxicity to the bacteria. In this study, toxicity of surfactants on Sphingomonas paucimobilis strain EPA505 and the effect on fluoranthene mineralization were investigated using Triton X-100 as model surfactant. The data showed that amendment with 0.48 mM (0.3 g l-1) of Triton X-100 completely inhibited fluoranthene and glucose mineralization and reduced cell culturability by 100% in 24 h. Electron micrographs indicate that Triton X-100 adversely affects the functioning of the cytoplasmic membrane. However, in the presence of 4.13 mM Ca(2+)-ions, Triton X-100 more than doubled the maximum fluoranthene mineralization rate and cell culturability was reduced by only 10%. In liquid cultures divalent ions, Ca2+ in particular and Mg2+ to a lesser extent, were thus shown to be essential for the surfactant-enhanced biodegradation of fluoranthene. Most likely the Ca(2+)-ions stabilized the cell membrane, making the cell less sensitive to Triton X-100. This is the first report on a specific factor which is important for successful surfactant-enhanced biodegradation of PAHs.

Biodegradation, Environmental↗
PubMed2004

The vascular anatomy of the digastric muscle.

There are plenty of flaps for the reconstruction of defects of the head and neck region. In the literature, local muscle and myocutaneous flaps such as sternocleidomastoid, pectoral, and deltopectoral flaps are proposed for obliteration of pharyngocutaneous fistulas. Restoration of facial nerve palsies in which nerve repair and nerve grafting are not feasible is accomplished by means of regional muscle transpositions. The vascular anatomy of the digastric muscle to be used in such instances is investigated after latex application to 18 neck regions of nine cadavers. The dissection continued anteriorly from the origin of the facial artery to the end of the submental artery, preserving all the branches piercing and nourishing the muscle. The submental artery courses over the posterior surface of the anterior belly of the digastric muscle, giving off the major pedicle of the muscle 1 cm after exiting behind the submandibular gland. The submental artery gives off another branch, the first minor pedicle of the muscle distal to the major pedicle at a distance of two thirds of the muscle length in a standard fashion in all the cadavers. The artery ends in the distal portion of the muscle, the second minor pedicle of the muscle. The artery gives off periosteal branches to the mandible after coursing through the insertion muscle. The anterior belly of the digastric muscle could be classified as a type II muscle, with a major pedicle and two minor pedicles, according to the system of Mathes and Nahai. The anterior digastric muscle can be a good alternative in obliteration of pharyngocutaneous fistulas, and defects of the mandible, including the body and angle of the mandible, can be amended with the split mandibular myo-osseous digastric flap.

Adult↗
PubMed2005

Fecal bacteria and sex hormones in soil and runoff from cropped watersheds amended with poultry litter.

The application of poultry litter to agricultural fields can provide plant nutrients for crops and forage production, but fecal bacteria and the sex hormones estradiol and testosterone are components of litter that can be detrimental to the environment. Our objective was to determine if applications of poultry litter to small watersheds would contribute to the load of fecal bacteria and sex hormones to soil and runoff. We, therefore, investigated the fate and transport of fecal bacteria, estradiol and testosterone from surface applied poultry litter to four small watersheds. Poultry litter was applied to meet the nitrogen requirements of pearl millet (Pennisetum glaucum L.) in 2000 and grain sorghum [Sorgham bicolor (L.) Moench] in 2001. Neither Salmonella nor Campylobacter were detected in the litter but the fecal indicator bacteria were. The average load of total coliforms,Escherichia coli, and fecal enterococci applied with the litter was 12.2, 11.9, and 12.7 log10 cells ha(−1), respectively. The average load of estradiol and testosterone was 3.1 and 0.09 mg ha(-1), respectively.Runoff events first occurred seven months after the first litter application in 2000, and three weeks after the second application in 2001.Only for the 25 July 2001 runoff event three weeks after the second litter application, were the concentrations of total coliforms, E. coli,and fecal enterococci in runoff greater than background concentrations which were on average 5.2, 1.1, and 2.9 log10 MPN 100 ml(−1),respectively [corrected]. Average background levels of total coliforms, fecal enterococci,and E. coli in surface soil were 8.2, 7.9, and 3.5 log (10) cells kg(−1) soil. At the rate of litter application the concentrations of estradiol and testosterone in the litter did not appear to impact the background levels in the soil and runoff. Because concentrations of sex hormones in litter from other broiler operations are known to be greater than in the litter we applied, further study on the connection between concentrations of sex hormones in poultry litter and operational practices is recommended.

Agriculture↗
PubMed2003

Dechlorination of chlorinated phenols by zero valent zinc.

Reductive dechlorination of chlorophenols (Pentachlorophenol, three tetrachlorophenols (TeCPs), six trichlorophenols (TCPs)) with zero valent zinc was examined through batch experiments. Zinc showed much higher reactivity towards PCP than iron and amended iron indicating that zero valent zinc can be a good candidate for reductive dechlorination of chlorinated phenols. Chlorophenols were sequentially dechlorinated and less chlorinated phenols were identified as reduction products. The mass balance was not complete, indicating that by-products are important and/or that products being measured were lost by unknown pathways. The dechlorination rate of the chlorinated phenols usually followed the order: PCP > TeCPs > TCPs. Among the TeCP and TCP isomers, the reactivity was in the order of 2,3,4,5-TeCP > 2,3,4,6-TeCP > 2,3,5,6-TeCP and 2,3,4-TCP > 2,3,6-TCP > 2,3,5-TCP > 2,4,6-TCP > 2,4,5-TCP > 3,4,5-TCP. The first order reaction rates varied by one order of magnitude or more, depending on the chlorines positions on a phenol ring. A regioselectivity was observed and daughter compound distributions could be rationalized by a mechanism in which radical intermediates were more stabilized by chlorine and hydroxyl groups than by hydrogen; positions alpha to the radical were found to be the most important in stabilization, followed by beta-positions.

Chlorine↗
PubMed2001

Genetic probes of three theories of maternal adjustment: II. Genetic and environmental influences.

This is the first report of the Twin Mom Study, an investigation of three hypotheses concerning influences on maternal adjustment. These hypotheses concern the role of the marital and parent-child relationships in mediating genetic influences on maternal adjustment and on the importance of the mothers' marital partners as a specifiable source of influences on their adjustment not shared with their sisters. The study's sample of 150 monozygotic (MZ) twins and 176 dizygotic (DZ) twins was drawn randomly from the Swedish Twin Registry and is, with some small exceptions, likely to be representative of women in the Swedish population. The sample included the marital partners of these twins and their adolescent children. Self-report and coded videotapes were a source of information about family process. Results reported in this first report focus on comparability of American and Swedish samples on scales measuring psychiatric symptoms, and on an analysis of genetic and environmental influences on nine measures of mothers' adjustment. Results suggest comparability between the US and Sweden. Genetic influences were found for all measures of adjustment, particularly in the psychological manifestations of anxiety and for smoking. The pattern of findings also underscored the importance of influences unique to each sibling within the twin pair, thus focusing attention on the potential role of marital partners in maternal adjustment. Results also suggested that experiences shared by the twin sisters, experiences unrelated to their genetic similarity, may influence their fearfulness and alcohol consumption. Our model did not include these influences and thus must be amended.

Adaptation, Psychological↗
PubMed1998

Occurrence of Vibrio vulnificus biotypes in Danish marine environments.

During the unusually warm summer in Denmark in 1994, 11 clinical cases of Vibrio vulnificus infection were reported. These reports initiated an investigation of the occurrence of V. vulnificus biotypes in Danish marine environments. Samples of coastal water, sediment, shellfish, and wild fish were analyzed by preenrichment in alkaline peptone water amended with polymyxin B (2.0 x 10(4) U/liter) followed by streaking onto modified cellobiose-polymyxin B-colistin agar. V. vulnificus-like colonies were tested with a V. vulnificus-specific DNA probe. Low densities of V. vulnificus were detected in water (0.8 to 19 CFU/liter) from June until mid-September and in sediment (0.04 to > 11 CFU/g) from July until mid-November. The presence of V. vulnificus was strongly correlated with water temperature. However, we isolated V. vulnificus from water from a mussel farm at a lower temperature than previously reported (7 degrees C). In 1 of the 13 locations studied, V. vulnificus was found in mussels in 7 of 17 samples analyzed; this is the first report of V. vulnificus in European shellfish. V. vulnificus was also isolated from gills, intestinal contents, and mucus from wild fish. Although biotyping of 706 V. vulnificus strains isolated during our investigations revealed that the majority of the strains (99.6%) belonged to biotype 1, biotype 2 was detected in seawater at a low frequency (0.4%). Our findings provide further evidence that seawater can serve as a reservoir and might facilitate spread of V. vulnificus biotype 2 to eels, with subsequent spread to persons handling eels. In conclusion, our data demonstrate that V. vulnificus is ubiquitous in a temperature marine environment and that V. vulnificus biotype 2 is not strictly confined to eels.

Animals↗
PubMed1992

Recurrent focal glomerulosclerosis: natural history and response to therapy.

PURPOSE: Recurrent focal glomerulosclerosis (FGS) has been well documented since it was first reported in 1972. However, the course of the disease after transplantation and the optimal treatment regimen have not been well defined since the introduction of newer treatment modalities. PATIENTS AND METHODS: We reviewed all the charts of patients with biospy-proven FGS who received renal transplants at our institution from January 1980 through December 1990. Case histories consistent with diagnoses other than primary FGS (such as reflux nephropathy or intravenous drug use) were eliminated from the study. During this time period, 78 allografts were received by 71 patients with FGS. Independent variables that were analyzed included sex, race, time in months between the diagnosis of FGS and end-stage disease (dialysis or transplantation), age at time of transplantation, type of dialysis, source of allograft (cadaveric or living related), haplotype matching, donor-specific transfusions, age and sex of the donor, post-transplantation acute tubular necrosis, rejection episodes, immunosuppression regimen, use of plasmapheresis and angiotensin converting enzyme (ACE) inhibitors, and outcome. RESULTS: FGS recurred in 25 allografts (32%) of 21 patients. Biopsy-proven diagnosis of recurrence was made a mean of 7.5 months (range: 0.5 to 44 months) after transplantation. Patients who had rapid progression to end-stage disease tended to experience more frequent recurrences. Of seven patients who received a second transplant, five patients lost the first graft to recurrent FGS, and four of those patients (80%) had a recurrence in the second allograft. Recurrent disease developed in 34% of patients concurrently treated with cyclosporine and in 28% of those treated with prednisone and azathioprine alone (NS). Patients with recurrent FGS who were treated with ACE inhibitors benefited from a significant reduction of proteinuria. Six patients underwent plasmapheresis after diagnosis of the recurrence. Three of five patients in whom the diagnosis was made early in the course of the disease and in whom plasmapheresis was initiated immediately had reversal of epithelial foot process effacement and remission of proteinuria. End-stage disease eventually developed in 14 allografts (56%) an average of 23.7 months (range: 1 to 65 months) after diagnosis of recurrent disease. The cause of failure was chronic rejection in four allografts and recurrent disease in the remaining 10 allografts. CONCLUSIONS: FGS recurs in approximately 30% of allografts and causes graft loss in half of these. Patients who have lost a first allograft to recurrent FGS are at high risk for developing recurrent disease in a second allograft. Prolonged allograft survival is possible in patients with recurrent FGS and may best be obtained with a combination of treatment modalities including cyclosporine (perhaps in higher dosages than are routinely used in clinical renal transplantation), ACE inhibitors, and early use of plasmapheresis. The efficacy of these modalities supports the notion that recurrent FGS is caused by a circulating humoral mediator.

Adolescent↗
PubMed1998

Microbial reductive dechlorination of aroclor 1260 in anaerobic slurries of estuarine sediments.

Reductive dechlorination of Aroclor 1260 was investigated in anaerobic slurries of estuarine sediments from Baltimore Harbor (Baltimore, Md.). The sediment slurries were amended with 800 ppm Aroclor 1260 with and without the addition of 350 muM 2,3,4,5-tetrachlorobiphenyl (2,3,4,5-CB) or 2,3,5,6-tetrachlorobiphenyl (2,3,5,6-CB) and incubated in triplicate at 30 degrees C under methanogenic conditions in an artificial estuarine medium. After 6 months, extensive meta dechlorination and moderate ortho dechlorination of Aroclor 1260 occurred in all incubated cultures except for sterilized controls. Overall, total chlorines per biphenyl decreased by up to 34%. meta chlorines per biphenyl decreased by 65, 55, and 45% and ortho chlorines declined by 18, 12, and 9%, respectively, when 2,3,4,5-CB, 2,3,5,6-CB, or no additional congener was supplied. This is the first confirmed report of microbial ortho dechlorination of a commercial polychlorinated biphenyl mixture. In addition, compared with incubated cultures supplied with Aroclor 1260 alone, the dechlorination of Aroclor 1260 plus 2,3,4,5-CB or 2,3,5,6-CB occurred with shorter lag times (31 to 60 days versus 90 days) and was more extensive, indicating that the addition of a single congener stimulated the dechlorination of Aroclor 1260.

Journal Article↗
PubMed1982

The EEC policy in the hazard assessment of new chemicals.

The sheer number of new chemicals produced each year poses problems to ensure that no dangerous products are brought in to use in the Community. Therefore the Council of Ministers of the European Communities has adopted on September 18, 1979 a Community legislation with respect to the notification of new chemicals. This is the so called sixth amendment of the Council directive of 27 June 1967 relating to the classification, packaging and labelling of dangerous substances. The purpose of this directive is to approximate the laws, regulations and administrative provisions of the ten Member States on: a) the notification of new chemical substances and b) the classification, packaging and labelling of substances dangerous to man and the environment which are placed on the market (including imported products) in the Member States of the Community. When giving this pre-marketing notification, the technical dossier requires, amongst others, the results of tests, of physico-chemical properties and toxicological and ecotoxicological parameters, following a three level hierarchical or step-sequence test system based on the quantities of the substances marketed. The first level concerns a mandatory base-set or level 0, the so called Annex VII, followed by a level 1 and level 2 testsystem (Annex VIII).

Animals↗
PubMed2005

Generating a taxonomy of regulatory responses to emerging issues in biomedicine.

In the biomedical field, calls for the generation of new regulations or for the amendment of existing regulations often follow the emergence of apparently new research practices (such as embryonic stem cell research), clinical practices (such as facial transplantation) and entities (such as Avian Influenza/'Bird Flu'). Calls for regulatory responses also arise as a result of controversies which bring to light longstanding practices, such as the call for increased regulation of human tissue collections that followed the discovery of unauthorised post-mortem organ retention. Whilst it seems obvious that new regulations should only be generated if existing regulations are inadequate (a practice referred to in this paper as 'regulatory syncretism'), this does not always occur in practice. This paper examines the conceptual steps involved in generating regulatory responses to emerging phenomena. Two decision points are identified. First, a stance is taken as to whether the emerging phenomenon raises unique ethical or legal issues (exceptionalism versus non-exceptionalism). Second, the decision is made as to whether new regulation should be generated only for truly unique phenomena (syncretism versus asyncretism). It is argued here that it is important to make a careful assessment of novelty, followed by a reflective and deliberative choice of regulatory syncretism or asyncretism, since each type of regulatory response has advantages which need to be harnessed and disadvantages which need to be managed--something that can only occur if regulators are attentive to the choices they are making.

Bioethical Issues↗
PubMed2004

An enzyme-coupled colorimetric assay for S-adenosylmethionine-dependent methyltransferases.

We report here an enzyme-coupled colorimetric assay for salicylic acid carboxyl methyltransferase (SAMT), which utilizes S-adenosyl-l-methionine (AdoMet or SAM) as the methyl donor. In this assay, S-adenosyl-l-homocysteine (AdoHcy or SAH), a common product of AdoMet-dependent transmethylation reactions, is first hydrolyzed by recombinant AdoHcy nucleosidase (EC 3.2.2.9) into adenine and S-ribosylhomocysteine. Recombinant LuxS (S-ribosylhomocysteinase, EC 3.2.1.148) cleaves the latter compound to form homocysteine. Finally, homocysteine is quantified using Ellman's reagent and the accompanying absorption change at 412nm through recording using a microplate format. Notably, SAMT and most AdoMet-dependent methyltransferases undergo marked AdoHcy-mediated product inhibition. As such, an additional advantage of this assay which includes AdoHcy nucleosidase is the destruction of AdoHcy, thus alleviating product inhibition. Under our assay conditions, complete substrate conversion is observed and precise kinetic parameters can be determined in a facile and quantitative manner. This assay should be generally applicable to other AdoMet-dependent methyltransferases. Moreover, the procedure is easily amendable to batch assay and high-throughput screening approaches.

Catalysis↗
PubMed2003

Voice beyond choice: hesitant voice in public debates about genetics in health care.

The rise of genetic techniques presents a great promise as well as some difficult dilemma's about how genetics will affect the way we will be able to live our lives. For this reason, in many countries, public debates are organized to reflect upon the development of predictive medicine. In this essay we focus on economist A. Hirschman's work on "exit, voice and loyalty" to analyse and enrich these public debates. We first introduce Hirschman's triad of concepts and focus on the concept of "voice," which refers to an institution's ability to allow clients to give feedback about products or services, and its ability to listen to the feedback given. We argue that voice is particularly important for the health care system in which predictive medicine is developing. Voice is crucial because how predictive medicine will become institutionalised is now in the process of becoming determined. However, in public debates about predictive medicine, voice tends to be reduced to providing people with the option of making a choice whether to use genetic techniques or not. We argue that this reduction of voice to choice is not very informative about predictive medicine and suggest an amendment of Hirschman's concept of voice, which we call "hesitant voice." Hesitant voice attempts to be informative about the uncertainty people experience in addressing predictive medicine and topicalises the gradual, the embodied, the tentative character of voice in developing situations like that of predictive medicine.

Choice Behavior↗
PubMed2005

Trace elements in agroecosystems and impacts on the environment.

Trace elements mean elements present at low concentrations (mg kg-1 or less) in agroecosystems. Some trace elements, including copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), molybdenum (Mo), and boron (B) are essential to plant growth and are called micronutrients. Except for B, these elements are also heavy metals, and are toxic to plants at high concentrations. Some trace elements, such as cobalt (Co) and selenium (Se), are not essential to plant growth but are required by animals and human beings. Other trace elements such as cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), mercury (Hg), and arsenic (As) have toxic effects on living organisms and are often considered as contaminants. Trace elements in an agroecosystem are either inherited from soil parent materials or inputs through human activities. Soil contamination with heavy metals and toxic elements due to parent materials or point sources often occurs in a limited area and is easy to identify. Repeated use of metal-enriched chemicals, fertilizers, and organic amendments such as sewage sludge as well as wastewater may cause contamination at a large scale. A good example is the increased concentration of Cu and Zn in soils under long-term production of citrus and other fruit crops. Many chemical processes are involved in the transformation of trace elements in soils, but precipitation-dissolution, adsorption-desorption, and complexation are the most important processes controlling bioavailability and mobility of trace elements in soils. Both deficiency and toxicity of trace elements occur in agroecosystems. Application of trace elements in fertilizers is effective in correcting micronutrient deficiencies for crop production, whereas remediation of soils contaminated with metals is still costly and difficult although phytoremediation appears promising as a cost-effective approach. Soil microorganisms are the first living organisms subjected to the impacts of metal contamination. Being responsive and sensitive, changes in microbial biomass, activity, and community structure as a result of increased metal concentration in soil may be used as indicators of soil contamination or soil environmental quality. Future research needs to focus on the balance of trace elements in an agroecosystem, elaboration of soil chemical and biochemical parameters that can be used to diagnose soil contamination with or deficiency in trace elements, and quantification of trace metal transport from an agroecosystem to the environment.

Adsorption↗