Xjenza Vol. 9 - 2004 - Needs Cover

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Xjenza 2004; Vol. 9

Brief Research Report MODELLING OF CALIX(4)ARENE SYSTEMS WITH UNUSUAL MECHANICAL PROPERTIES* Jennifer J. Williams and Joseph N. Grima† Department of Chemistry, University of Malta, Msida, Malta. www: http://staff.um.edu.mt/jgri1

Kenneth E. Evans Department of Engineering, University of Exeter, Exeter, UK.

Auxetic materials exhibit the very unusual property of becoming wider when stretched and narrower when squashed [1], that is they have a negative Poisson’s ratio (Fig. 1). This counter-intuitive behaviour results in many beneficial effects in the materials’ properties that make auxetics superior to conventional materials in many practical applications [2]. In recent years, a number of auxetics have been manufactured by modification of the microstructure of existing materials [3], and a number of molecular level auxetics have also been proposed [1,4].

Figure 1: Illustration of conventional (non-auxetic) vs. auxetic behaviour.

Force-field based molecular modelling simulations have been used to investigate the potential of calix(4)arenes (Fig. 2) as building blocks for a novel class of molecular level auxetics. This newly proposed auxetic system, henceforth referred to as a calix(4)arene network (Fig. 3), offers the advantage over a number of previously proposed systems that it is made up of readily available sub-units, i.e. calix(4)arenes, the chemistry of which have been extensively investigated in recent years [5].

Figure 2: The structure of the simplest single calix: tetrahydroxycalix(4)arene as a) a sketch and b) constructed in the Cerius2 Graphical Interface.

Figure 3: The unit cell of the calix(4)arene network as a) a sketch and b) constructed in the Cerius2 Graphical Interface.

In particular, an optimal methodology for the modelling and property prediction of calixarene systems was developed and validated.

The development of a methodology was essential since no standard procedure is as yet available for the modelling of novel calixarene networks. The PCFF force-field within the commercially available molecular modelling software Cerius2 [6] was identified as the most suitable for the modelling of calixarene systems. The Second Derivative method [6] was found to give accurate predictions of mechanical

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

†

Corresponding Author. Tel: +356 2340-2274 / 5, e-mail: joseph.grima@um.edu.mt

2 properties. The optimised methodology was then applied to a number of structural variants of the basic calixarene network. Negative Poisson’s ratios, that is auxetic behaviour, was demonstrated in the majority of networks considered.

Given the many benefits of materials with negative Poisson’s ratios, it is hoped that these systems would be synthesised and commercialised shortly.

References: [1] K. E. Evans, M. A. Nkansah, I. J. Hutchinson and S. C Rogers, Nature, 353 (1991) 124.

[2] J. N. Grima, University of Malta Annual Report (2002); N. Chan and K.E. Evans, J. Cell. Plast, 34 (1998) 231; B. D. Caddock and K.E. Evans, Biomaterials, 16 (1995) 1109; J. B. Choi and R. S. Lakes, Cellular Polymers, 10 (1991) 205.

[3] R. S. Lakes, Science, 235 (1987) 1038; K. L. Alderson and K. E. Evans, Polymer, 33 (1992) 4435; K.E. Evans and B. D. Caddock J. Phys. D: Appl.

Phys. 22, (1989) 1883; K. E. Evans, M. A. Nkansah and I. J. Hutchinson, Acta Metal. Mater., 42 (1994) 1289.

[4] J. N. Grima and K. E. Evans J. Mat. Sci. Lett., 19 (2000) 1563; J. N. Grima and K. E. Evans, ACS Polymeric Materials Science & Engineering Preprints, 83 (2000) 367; J. N. Grima, and K.E. Evans, Chem. Comm., (2000) 1531; J. N. Grima, R. Jackson, A. Anderson and K. E. Evans Adv. Mater., 12, (2000) 1912; R. H. Baughman, D. S. Galvao, C. Cui and S. O. Dantas, Chem. Phys. Lett, 269 (1997) 356.

[5] C. D. Gutsche, Calixarenes Revisited, (1998), Royal Society of Chemistry: Cambridge, U.K.; V. Bohmer and J. Vicens (eds) (1990) Topics in Inclusion phenomena, Calixarenes, A Versatile Class of Macrocyclic Compounds, Kluwer Academis Dordrecht.; L. Mandolini and U. Ungaro (eds) Calixarenes In Action, (2000) Imperial College Press: London, U.K. [6] Molecular Simulations Inc. (MSI), San Diego, California, currently incorporated within Accelrys (http://www.accelrys.com).

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Xjenza 2004; Vol. 9

Brief Research Report MOLECULAR MODELLING OF AUXETIC ZEOLITES* Michelle Wood and Joseph N. Grima† Department of Chemistry, University of Malta, Msida, Malta. www: http://staff.um.edu.mt/jgri1

Kenneth E. Evans Department of Engineering, University of Exeter, Exeter, UK.

Andrew Alderson Centre for Materials Research and Innovation, Bolton Institute, Bolton, UK.

Materials with a negative Poisson’s ratio, i.e. auxetic materials, exhibit the unexpected property of becoming wider when stretched and thinner when compressed (Fig. 1) [1]. This rare property, which is very much dependent on the geometry of the material, results in the enhancement of various macroscopic properties of the material and makes auxetics superior to their conventional counterparts in many practical applications [2].

Load

b) Auxetic material

Load

Load

Load

a) Conventional Material

Oxj

Oxi

v ij = −

εj − ve = + ve =− εi + ve

v ij = −

εj + ve = − ve = − εi + ve

Figure 1: Comparison of the effect of stretching on a) a conventional material, and b) an auxetic material. The dotted lines represented the original shapes.

It was recently shown through preliminary modelling studies [3] that some zeolite frameworks may exhibit this unusual property. The preliminary research on zeolites had defined that those zeolites that exhibit auxetic properties deform via particular mechanisms in response to applied stress. These include the rotating squares mechanism and the rotating triangles mechanism, where the corners of the squares or triangles are oxygen atoms [4].

Unfortunately, these preliminary studies relied on various assumptions, e.g. no cations or interstitial water molecules were included, assuming therefore that such species would have little or no effect on the deformation mechanism.

This paper re-examines this problem and a methodology for simulating zeolites with cations and water molecules is described. This methodology was applied on a number of zeolites with the scope of assessing the contribution of cations and water molecules on the mechanical properties and on the way the system responds to applied loads (i.e. the deformation mechanism). The study was conducted using molecular modelling i.e. techniques of visualisation and computational methods in order to study or predict the properties of molecules. The zeolite structures were simulated through force-field based simulations using the commercially available molecular modelling software Cerius2 [5]. In particular, two zeolites were studied, NAT and EDI which in the preliminary study were found to exhibit auxetic behaviour through a rotating squares mechanism (Figure 2).

Figure 2: The rotating squares mechanism observed in the zeolite: NAT in the (001) plane.

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

†

Corresponding Author. Tel: +356 2340-2274 / 5, e-mail: joseph.grima@um.edu.mt

4

It was found that cations and water molecules do play an important role on the Poisson’s ratios although in most cases, the auxetic behaviour is retained. While cations reduced the auxeticity of the structure by a small degree, the addition of water molecules had a greater effect rendering the structures less auxetic to the extent that auxeticity is only observed off-axis (see Fig. 3).

This observation may be explained by the fact that the structures were also observed to be stiffer with the inclusion of water and cations. Essentially, the water and cations seemed to be ‘in the way’, preventing the ‘hinging oxygen atoms’ from deforming as much as was possible in response to loading.

Fig. 3: The ‘reduced’ auxeticity in NAT as the amount of interstitial species is increased. Note that whilst the SiO2 equilvealent of NAT without any interstitial species is auxetic for loading in any direction in the (001)-plane (the xy-plane), the real zeoilite (i.e.

NAT framework + cations and water) is only predicted to be auxetic at 45o off-axis.

The discovery that some zeolites exhibit a negative Poisson’s ratio is likely to have various important commercial repercussions, and, in particular, the possibility of having molecular sieves where the pore size can be controlled is more likely to become a reality [6].

References: [1] K. E. Evans, M. A. Nkansah, I. J. Hutchinson and S. C Rogers, Nature, 353 (1991) 124.

[2] J.N. Grima, University of Malta Annual Report, 2002.

[3] J. N. Grima, R. Jackson, A. Alderson and K. E. Evans Adv. Mater., 12 (2000) 1912.

[4] J. N. Grima and K. E. Evans J. Mat. Sci. Lett., 19 (2000) 1563-1565.

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[5] Molecular Simulations Inc. (MSI), San Diego, California, currently incorporated within Accelrys (http://www.accelrys.com).

[6] A. Alderson, J. Rasburn, K.E. Evans, J.N. Grima, Membrane Technology, 137 (2001) p. 6-8.

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Xjenza 2004; Vol. 9

Brief Research Report ADSORPTION AND ADSOLUBILISATION OF ORGANOTINS ONTO SILICA* Daniel A. Vella Malta Centre for Restoration, Bighi, Kalkara, CSP12, Malta

Emmanuel Sinagra†Department of Chemistry, University of Malta, Msida, Malta. www: http://staff.um.edu.mt/msin1

The adsorption of organotins bis-tributyltin oxide (TBT), tripentyltin chloride (TPeT), tripropyltin chloride (TPrT), dibutyltin dichloride (DBT) and butyltin trichloride (MBT) onto a model silica surface at pH 5.2 and 0.4M NaCl was investigated in the presence of the non-ionic surfactant Triton X-100 (TX-100). For the trialkyltin series (i.e. TBT, TPeT and TPrT), adsolubilisation onto the surface was observed for the more lipophilic species TPeT and TBT at equilibrium surfactant concentrations below the critical micellar concentration (CMC) of TX100. This was not observed for TPrT, possibly because of the lower lipophilic character of this compound as a result of its smaller sized alkyl chain groups.

Solubilisation within micelles above an equilibrium surfactant concentration in excess of the CMC was however observed for all trialkyltin compounds investigated. Solubilisation of the three trialkyl tin species studied followed the trend TPeT > T BT > TPrT.

In contrast to trialkyltins, adsorption of DBT onto the silica surface was complete and unaffected by the presence of the surfactant. The behaviour of DBT in this system could be explained by assuming the formation of doubly charged dibutyltin cations (Bu2Sn2+).

Unlike DBT, adsorption of MBT was affected by the presence of TX-100. At surfactant concentrations in excess of the CMC, the formation of micelles was found to slow down MBT adsorption onto silica, possibly via a solubilisation phenomenon.

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

â€

Corresponding Author. Tel: +356 2340 2396, e-mail: emmanuel.sinagra@um.edu.mt

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Xjenza 2004; Vol. 9

Brief Research Report GELATIN NANOPARTICLE PRODUCTION: AN IN-PROCESS STUDY USING SIZE EXCLUSION CHROMATOGRAPHY * Jurgen Mifsud and Emmanuel Sinagra Department of Chemistry, University of Malta, Msida, Malta. www: http://staff.um.edu.mt/msin1

Claude A. Farrugia† Chemistry Department, Junior College, University of Malta, Msida MSD 06, Malta

Gelatin, a naturally occurring polypeptide, is a good candidate for the preparation of nanoparticles, and a method for reproducibly preparing nanoparticles from gelatin has been described [1]. The objective of this study was to carry out in-process development of the method by characterising the molecular weights of the species present in solution at various stages of the production using size exclusion HPLC. Gelatin nanoparticles were prepared according to the method described by Farrugia and Groves [1]. Briefly, colloidal dispersions of gelatin were produced by desolvation of dilute aqueous solutions of B225 gelatin with 70% w/w ethanol at 37°C. The colloidal particles were then crosslinked with 1% w/w glutaraldehyde; excess glutaraldehyde was neutralised by the addition of sodium metabisulfite solution. Separation and purification of the nanoparticles was performed by ultrafiltration, using distilled water as the washing agent.

Samples from various stages throughout the nanoparticle production were filtered through 0.2-µm filters, and analysed by HPLC on a Waters™ Ultrahydrogel Linear size exclusion column at 29°C, using phosphate-buffered saline mobile phase at a flow rate of 0.3 mL min-1, and a tuneable absorbance detector set at 205nm.

Addition of the non-solvent ethanol to the initial gelatin solution resulted in removal of all but the low molecular weight species, the original gelatin solution having a characteristic broad peak extending from approximately 22 to 36 minutes of elution time while the filtered desolvated solution contained a much lower concentration of gelatin species with retention times

between 27 to 36 minutes. These results are consistent with those observed in earlier studies [1]. However, these residual soluble species were not present in the final nanoparticle dispersion, as filtrates of the nanoparticle dispersion did not exhibit any significant concentrations of eluted species, while the ultrafiltrate washings only contained species with retention times greater than approximately 34 minutes. The chromatogram of a water control taken through the nanoparticle production process was practically superimposable on that of the filtered nanoparticle dispersion, indicating that the soluble gelatin species present post-desolvation were effectively absent following cross-linking and neutralisation. An explanation for this observation is that the glutaraldehyde crosslinked both the desolvated and the soluble gelatin, a hypothesis supported by the fact that crosslinking of an undesolvated gelatin solution also did not have any residual detectable gelatin species. The residual gelatin species following desolvation thus appear to be crosslinked onto the surface of previously existing nanoparticles (nanoencapsulation), possibly establishing a gelatin ‘brush border’ and accounting for the dispersion stability of the nanoparticles [2].

Ultrafiltration appeared to be an effective method for separation and purification of the nanoparticles. The glutaraldehyde-metabisulfite addition product formed during the neutralisation process was present in the first ultrafiltrate of both the nanoparticle and control preparations, which exhibited a sharp absorption peak at high retention times. This peak was practically absent in the third ultrafiltrate and also in the filtered nanoparticle preparation, indicating its removal from the nanoparticle

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

†

Corresponding Author. Tel: +356 2590-7215, E-mail: claude.farrugia@um.edu.mt

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Xjenza (2004)

dispersion. The effectiveness of the ultrafiltration process at removing gelatin species should theoretically not have been of any direct concern, since nanoparticle dispersions did not appear to contain any significant amount of residual gelatin species, as described above, and dispersed gelatin nanoparticles incubated in aqueous media did not appear to undergo any hydrolysis to release soluble gelatin that could be detected by HPLC. Nevertheless, ultrafiltration of dilute gelatin solutions was shown to be effective at removing gelatin species of low to intermediate molecular weights, with medium to high molecular weight species being detected in the retentate.

We have therefore concluded that, during nanoparticle production, the crosslinking process not only crosslinks the colloidal gelatin particles but also removes residual soluble gelatin fractions from solution, probably by crosslinking to the surface of the existing nanoparticles.

The ultrafiltration process is effective both at removing the addition reaction impurities and at removing low molecular weight gelatin species. However, the latter do not appear to be present in the nanoparticle dispersion prior to purification.

References: [1]

C.A. Farrugia and M.J. Groves, J. Pharm.

Pharmacol., 51 (1999) 643.

[2]

J. Mifsud, ‘Production and Stability of Gelatin Nanoparticles’, M.Sc. Dissertation, University of Malta, (2003).

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Xjenza 2004; Vol. 9

Brief Research Report THE COSTS OF ACCREDITATION FOR SMALL ANALYTICAL CHEMICAL LABORATORIES * George Peplow†and Leila Valenzia Department of Chemistry, University of Malta, Msida, Malta.

Quality assurance programmes for laboratory accreditation must be fairly judged (benefits derived vs costs involved), especially for small laboratories with their limited market potential. Costs are tangible and not too difficult to assess, but most of the benefits are intangible, and evaluating their importance involves subjective judgements [1,2].

Large analytical laboratories perform a comparatively small range of test parameters compared to the number of samples. The frequency of testing is regular by virtue of their capacity. Small laboratories typically handle a small number of samples for a wide variety of test parameters.

The submission of samples is intermittent, and the laboratory must continuously strive to retain the availability of clients within a limited market, especially in small states or regions. The relationship between the number of samples, number of test parameters and the cost of pro-rata man-hours handled by a laboratory are considered in this presentation. The influence of in/frequent samples on the laboratory costs determines the feasibility for a laboratory to render its services competitively in the market.

The analysis time taken to carry out test measurements (expressed in man-hours) affects the operational costs, and for multifarious measurements in a small laboratory the analysis time is longer. Small laboratories face higher costs for the mean pro-rata man-hours than larger laboratories.

In order to succeed in the market, laboratories have to produce more results in a shorter time at a lower cost. At the same time they must provide results of an adequate quality as required by accreditation, which involves additional effort.

The public image of a service laboratory, the need for service improvement, the effect of government laws and regulations, and the complaints from customers are examples of items that cannot be ignored. A laboratory quality assurance programme must consider such matters as part of the overall plan.

However, there are three major cost areas related to quality; prevention costs, appraisal costs and correction costs [2]. The cost of accreditation is an important issue for the laboratories since they have to compete in the measurement, testing and analytical market of today. The initial costs of accreditation and the running costs of regular re-assessments are a matter of concern for small laboratories, especially because of the limitation they have due to the market availability and competition.

Accreditation costs are an important economic factor since the costs are about 10-15% of the overall costs for a laboratory preparing for accreditation [3]. It is also possible, that small analytical laboratories may encounter high relative costs of accreditation as a result of being situated in regions or states where the market volume is constrained [4].

Although accreditation provides a formal guarantee that a laboratory is able to produce reliable results it does not provide a real competitive advantage [5]. Small laboratories must strike a balance between the costs that accreditation entails, including initial costs to set up the quality system, running costs of the routine requirements of accreditation, and the regular costs for external reassessments. It is the laboratory management that must evaluate the advantages, costs and benefits and decide about feasibility of accreditation.

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

â€

Corresponding Author. +356 2340 2276, E-mail: peplowg@maltanet.net

9 References: [1] H. Gunzler, ‘Accreditation and Quality Assurance in Analytical Chemistry’, (1996), Springer-Verlag, Berlin Heidelberg, p. 74.

[2] F.M. Garfield, ‘Quality Assurance Principles for Analytical Laboratories’, (1996), AOAC International, p. 4-5.

[3] EUROLAB aisbl; European Federation of National Associations of Measurement, Testing and Analytical Laboratories; Cost of accreditation; EL/11-01/00/363; Technical Report No. 1/2000; May 2000.

[4] EUROLAB aisbl; European Federation of National Associations of Measurements, Testing and Analytical Laboratories; Satisfaction of customers with European accreditation bodies; EL/11/01/02/968; Technical Report No. 2/2002; December 2002.

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Xjenza 2004; Vol. 9

Brief Research Report VOLATILE ORGANIC COMPOUNDS IN STREET AIR * David G. Saliba and Alfred J. Vella† Department of Chemistry, University of Malta, Msida, Malta.

Volatile Organic Compounds (VOCs) are organic compounds which are released to the atmosphere by various industrial sources or through vaporization of oil products. VOCs are chemically reactive and are involved in the chemistry of tropospheric ozone production.

VOCs derived from gasoline combustion and evaporation have deleterious effects on human health [1]. This paper presents the results from a quantitative study on street air pollution from specific VOC compounds, namely benzene, toluene, ethylbenzene, ortho- meta- paraxylenes, methyl tert-butyl ether, tert- amyl methyl ether (TAME), ethyl tert- butyl methyl ether (ETBE), 2methylpentane, 3-methyl pentane and isooctane as found in street air in Malta in the months of January to April 2001 and, in particular, how the street air pollution was affected by the activities of fuel service stations (FSS).

VOCs in air were adsorbed onto charcoal sorbents which were then extracted with carbon disulphide. The resulting solution was analysed by gas chromatography/flame ionisation detection (GC/FID).

Ambient air levels of benzene and toluene away from FSS ranged from 10.5 µg m-3 to 57.2 µg m-3 and 6.3 µg m-3 to 30.1 µg m-3 respectively. The risk criterion proposed by the World Health Organisation, which considers as “socially acceptable” the risk of 22 to 37 additional cases of leukaemia every million people, is equivalent to a concentration of 5 µg m-3 benzene, and as a consequence was set as the limit concentration for urban air [2].

Active air samples were taken from Hamrun, Paola, Mosta and Msida. These locations represent densely populated urban zones with main arterial roads that are not in the vicinity of FSS. Passive air samples were taken from Hamrun, Birkirkara and Qormi. These represent areas having FSS amidst densely populated urban zones.

Figure 1: A map of Malta showing the Sampling Locations

This study found a strong correlation between wind speed and VOC concentration in Hamrun (r2 = 0.9329) and Paola (r2 = 0.8542) while no such correlation was found in Mosta (r2 = 0.2816) and Msida (r2 = 0.3129).

This study also found a clear diminishing trend of pollutant air concentration with distance from FSS (benzene: 140.3 µg m-3 at the forecourt of the Qormi service station, decreasing to 15.8 µg m-3 130 m down the road).

A sharp shift in the ambient air benzene/toluene (B/T) ratio from 0.25 in Sliema and 0.32 in Msida in 1999 [3] to 1.80 at both sites as measured in this study was observed. The main reason for this observation is likely to be the increased quantity of benzene found in premium gasoline introduced to the market during the period of this study (the B/T ratio in liquid gasoline increased from 0.170 (1999) to 0.896 (2001)).

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

†

Corresponding Author. Tel. +356 2340 2275 e-mail: alfred.j.vella@um.edu.mt

11 The values of the mole fraction of ethylbenzene (φE) expressed in terms of the isomeric mixture of compounds (ethylbenzene and xylenes) for air samples in the vicinity of the Qormi fuel service station range from 0.22-0.30 (Mean 0.28; CV 8.8%) and this compares well with a value of 0.29 for headspace gas above liquid gasoline.

This strongly suggests gasoline evaporative emissions as the main source of VOC pollution in the vicinity of the FSS. The value of (φE) for air samples away from FSS ranged from 0.14 – 0.27 (Mean 0.18; CV 17%). This strongly suggests a separate source of VOC pollution away from FSS, probably vehicular, tailpipe emissions.

References: [1] Human Health Work Group New York State Department of Environmental Conservation Comparative Risk Project (2001) 124 –132.

[2] Fondazione Salvatore Maugeri, Padova, Italy Macbeth (Monitoring of Atmospheric Concentration of Benzene in European Towns and Homes) Programme (1999) [3] Zammit M. Influence of Service stations on Air Quality, B.Sc. (Hons) Dissertation, University of Malta (1999)

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Xjenza 2004; Vol. 9

Brief Research Report ENVIRONMENTAL FATE OF TRIASULFURON IN SOILS AMENDED WITH MUNICIPAL WASTE COMPOST * Daniel Said-Pullicino and Alfred J. Vella Department of Chemistry, University of Malta, Msida, Malta.

Giovanni Gigliotti† Dipartimento di Scienze Agroambientali e della Produzione Vegetale, Università di Perugia, Italy. .

The rate of degradation in amended and non-amended soils is explained by a two-stage degradation kinetics.

During the initial phase, although triasulfuron degradation was rapid with a half-life of ≈30d (Table 1), the presence of compost and HoDOM was found to slightly reduce the rate of degradation with respect to that in non-amended soil. (a)

(b)

0.60

0.60 Soil + compost (90t/ha)

Soil + compost (90t/ha)

Soil + compost (30t/ha)

Soil + compost (30t/ha)

0.50

0.50

Soil

x/m (µg g-1)

0.40

-1

x/m (µg g )

Source-separated municipal waste compost (MWC) is often used in agriculture as an organic amendment in order to improve physical and chemical soil fertility.

Recently, increased interest has been shown to the understanding of how the application of MWC may influence the behaviour of xenobiotics in the soil system.

The amendment of soil with compost may significantly influence the mobility and persistence of pesticides and thus affect their environmental fate. Factors like adsorption, kinetics and rate of degradation of pesticides could be altered in amended soils.

0.30 0.20

0.00 0.00

1.00

2.00

3.00

0.20

4.00

0.00 0.00

5.00

1.00

-1

0.60

0.50

3.00

4.00

5.00

4.00

5.00

0.60 Soil + HA Soil + FA Soil + HoDOM Soil

0.50

-1

x/m (µg g-1)

0.40

0.30

0.20

0.00 0.00

2.00

C e (µg mL-1)

C e (µg mL ) Soil + HA Soil + FA Soil + HoDOM Soil

0.40 0.30 0.20 0.10

0.10

Results have shown that the adsorption of triasulfuron to soil increases in the presence of compost, and that the HA and HoDOM fractions are mainly responsible for this increase (Fig. 1). HoDOM applied to the soils underwent sorption reactions with the soils and in the sorbed state, served to increase the adsorption capacity of the soil for triasulfuron. The rate of hydrolysis of triasulfuron in solution was significantly higher at acidic pH and the presence of organic matter fractions extracted from compost also slightly increased the rate of hydrolysis.

0.30

0.10

0.10

x/m (µg g )

The main objective of this study was to determine the effects of the addition of compost made from sourceseparated municipal waste and green waste, on the fate of triasulfuron, a sulfonylurea herbicide utilized in the postemergence treatment of cereals. Two native soils with low organic matter content were used. A series of analyses was carried out to evaluate the adsorption and degradation of the herbicide in soil and in solution after the addition of compost and compost-extracted organic fractions namely humic acids (HA), fulvic acids (FA) and hydrophobic dissolved organic matter (HoDOM).

Soil

0.40

1.00

2.00

3.00

4.00

5.00

0.00 0.00

-1

C e (µg mL )

1.00

2.00

3.00 -1

C e (µg mL )

Figure 1: Adsorption isotherms of triasulfuron on (a) Filoncia and (b) Molinaccio soils in the presence and absence of compost, HA, FA and HoDOM. Error bars represent SE.

*

Paper presented at the Second National Chemistry Symposium, Malta, March 2004.

†

Corresponding Author. E-mail: gigliott@unipg.it

13

Xjenza (2004) k ×10-3†

t½†

r2

day-1

day

dimensionless

Filoncia + compost + HoDOM

36 ± 2 31 ± 1 28 ± 1

19.3 ± 1.4 22.5 ± 1.1 25.0 ± 1.2

0.9860 0.9936 0.9937

Molinaccio + compost + HoDOM

35 ± 2 30 ± 2 28 ± 1

19.6 ± 1.4 23.4 ± 2.0 25.2 ± 1.2

0.9863 0.9811 0.9940

Soil

† Value ± 95% Confidence interval.

Table 1: Degradation of triasulfuron in amended and non-amended soil during the first 25 days.