Mercury (Hg) methylation was studied in water,sediment and Eichhornia crassipesroots of a freshwater lake, in Rio de Janeiro(Brazil). Samples were incubated with²⁰³HgCl₂ and the Me²⁰³Hg producedwas measured by liquid scintillation.Methylmercury (MeHg) production was <10⁻³% in water, low in sediment (up to5.8%) and high in E. crassipesroots (21–27%). Higher MeHg formation wasfound in aerobic conditions for the roots and inanaerobic conditions for the sediment.Methylation increased with incubation time, upto 5 days. A 3-day incubation period was used inthe majority of the assays, to avoid large scalephysico-chemical changes inside the incubationflasks. Methylation was not detected inheat-sterilized root samples. Sodium sulphatestimulated Hg methylation while sodium molybdateinhibited the process in samples incubated for3, 6, 12, 24, 48 and 72 hr. This suggeststhat sulphidogenic bacteria are responsible forthe methylation process. Experiments with rootsstored at 5 and 25 °C fordifferent periods before incubation, indicatethat methylation is modified by storage time and temperature.

The water quality of a stream affected by miningactivities was investigated on the basis of a mineralogical studyfor the related solids, and their subsequent changes weremonitored for a year, so as to clarify the impact of the acidmine drainage (AMD) to the stream. The mine-affected stream wasclassified into Ca–Mg and sulfate type, and the concentrations ofits major constituents ranged from tens to hundreds times higherthan those of the background stream. This was most likely due toacid-generating reactions involving the oxidation of sulfides inthe mineralized zone, and subsequent neutralizations involvingcalcite and chlorite as possible sources of Ca and Mg,respectively. This interpretation is consistent with thethermodynamic and mass-balance calculations. The concentrationsof the dissolved constituents changed seasonally, dependinglargely on rainfall in the mine-affected stream. However, thedramatic decrease in the ratio of Mg/Ca, independent of rainfall,indicates that some changes did occur in sources, including theheterogeneous distribution of main source materials, the changein chemical conditions, especially in pH, pe(Eh), and PCO ₂,in the reacting fluid, and the consequential solubility changesin sources. In spite of the limitations of short-term monitoring,it does provide some meaningful information in order to constructa long-term monitoring program.

Polycyclic aromatic hydrocarbon and heavymetal (Pb, Cd, Cu, Zn, Hg, Fe, Co, Cr, Mo) contentswere established in soil and plant samples collectedin different areas of the railway junction IławaGłówna, Poland. Soil and plant samples werecollected in four functional parts of the junction, i.e. the loading ramp, platform area, rolling stockcleaning bay and the railway siding. It was found thatthe PAH contamination of soil and plants was thehighest in the platform area and near the railwaysiding and lowest in the loading ramp and cleaning bayareas. The contamination exceeded control levels up toalmost twenty fold. The heavy metal contaminationpattern was different. The soil and plants were veryhighly contaminated in the cleaning bay and side trackareas while the loading ramp and platform areas wereless contaminated. A particularly high pollution levelwas observed for mercury in the cleaning bay area.Also lead, zinc and copper pollution levels wererelatively high in the cleaning bay and side trackareas. No significant increase in molybdenum contentwas observed in comparison with the control area.

Water and sediment quality in threetidal bayous located near Pensacola, Florida, wereassessed during 1993–1995. The primary objective wasto determine the environmental condition of therelatively small urban bayous by comparing thechemical quality of the sediments and surface waterwith published guidelines and criteria developed toprotect marine life. Surface water concentrations ofmost potential toxicants such as heavy metals,organochloride pesticides, PAHs and PCBs were usuallybelow method detection limits. The major exception tothis trend was for copper which consistently exceededFlorida and National acute and chronic water qualitycriteria. Nickel, cadmium and chromium intermittentlyexceeded these criteria. Sediment contamination wassite-specific and chemically diverse. Theconcentrations of as many as 17 compounds exceededproposed Florida sediment quality assessmentguidelines indicating the potential for adversebiological effects. Nutrient concentrations, with oneexception, were below average levels found in otherFlorida estuaries. Seasonal variation in contaminantconcentrations for sediment collected from the samesampling station was less than an order of magnitude. The differences in the concentrations of the sameanalytes as measured for the multiple samplingstations located within the same bayou varied 1 to 2orders of magnitude and over 2 orders of magnitude forthe 20 sampling stations located in the three bayous. A within-bayou sediment contaminant gradient wasevident; sediment quality generally improved seaward.

Our field survey showed that thequality of shallow groundwater around the KatsuraRiver in the Kyoto Basin was strongly affected by theinfiltration of river water. Furthermore, that thedeterioration of the groundwater in the southern areato the west of the Katsura River may be related to theincrease in groundwater extraction. To clarify themechanism of groundwater deterioration, we havedeveloped a stochastic method to simulate groundwaterflow. The results showed that there was a largereduction in the groundwater level where groundwaterextraction was intense and recharge flowed from theKatsura River to the high extraction areas in thesouthern region. Another simulation showed that if thegroundwater extraction was 10% of the present removalrate, there would be little recharge from the KatsuraRiver into the groundwater and the quality of thegroundwater would be improved. Thus, we conclude thatthe cause of groundwater deterioration is probably dueto the induced recharge of deteriorated river waterfrom the Katsura River.

Twenty-eight volatile organic compounds have been measured in a 3-month monitoring campaign. The sampling point is locatedin the urban centre of La Coruña, a medium-size town in theNorthwest of Spain. Only a petrol refinery can be consideredas an important point VOCs source in its surrounding area.The municipal landfill collapsed in September 1996, and rebuilding works caused strong odour episodes at the urbancentre. We tried to check how this problem affected urban airquality. Samples were taken with Tenax-TA tubes and analysedby thermal desorption-GC-MS. From the results obtained, traffic emissions were recognised as the main VOCs source inthe sampling zone. On November 9th a contaminationepisode took place. Aromatic and aliphatic compounds levelswere probably affected by emissions from fuel treatmentprocesses in a nearby petrol refinery. No influence onquantified VOCs concentrations from the remaking landfillworks was observed. Several compounds (organosulphurs, estersand alcohols) were recognised as the cause of odour problems.

The maintenance of safe-drivingconditions in snow and ice-affected areas in thewintertime includes the use of sodium chloride (NaCl)as de-icing salts. In this study, the impact of NaClon soil-colloid mobilisation and exchangeablebase-cation leaching has been evaluated. The chemistryof groundwater samples below an infiltration trenchfor highway runoff and leachate from column studiessuggested that soil-colloid mobilisation had occurred,as the exchangeable sodium (Na) concentration and theelectrical conductivity (EC) in the groundwater/columnleachate reached the threshold values for colloiddispersion. Generally, samples with no dispersionproblems had high Na and calcium (Ca) concentrations,suggesting that the initial effect of the de-icingsalt was to stabilise the colloids. In the columnstudy there was a good agreement between the degree ofcolloid dipersion problems and lead (Pb) concentrationwhen the pH value was above 7.0. Significant negativecorrelations between Na/CEC (cation exchange capacity)and Ca/CEC in roadside soils from three sitesindicated that Na preferentially displaces Ca from theexchange sites. However, the groundwater dataindicated that Na ions also displace potassium (K) andmagnesium (Mg). A positive effect of NaCl seen at onesite was an increase in the K concentration, which ishighly likely an effect of Na ions displacing fixed Kbetween the layers of 2:1 type clay minerals. In soilslacking these types of clay minerals, severe Kshortage may result from a high plant demand combinedwith the low K concentration in the readily availablefractions in the original soil and a highsusceptibility to leaching. The most significantimpact on soil exchange processes was found to occurwithin 6 m from the road.

Subsurface tile drainage systems with drainspacings of 15 m in 0.4 ha and 25 m in 3.2 ha wereinstalled at the farmers' field in 1986 and 1987,respectively, to study their effect on the reclamationof the coastal saline sodic clay soils. The system'sperformance in terms of the changing physical andchemical properties of the soil and rice yield wascontinuously monitored for a decade. Field datasuggested the possibility of adopting wider drainspacings and thus, drainage system with 35 and 55 mspacings was laid in 1997 in a 4 ha area. On theseinstallations the losses of NH₄ ⁺-N throughsub-surface drainage effluent were estimated. Thearea under 25 m drain spacing was the control with nocrops, fertilization and irrigation. Analysis ofwater samples collected daily for 10 days startingfrom 40 DAT from the drain laterals revealed thatthere were no trace of NH₄ ⁺-N in theeffluent from 15 and 25 m drain spacings. However,the effluent from 35 and 55 m spacings contained anaverage of 6.704 mg L⁻¹ and 4.205 mg L⁻¹ of NH₄ ⁺-N, respectively, before irrigation and2.438 and 1.650 mg L⁻¹ after irrigation. Themagnitudes of the losses of NH₄ ⁺-N duringthe crop season were 6.43 kg ha⁻¹ in 35 m spacingwith a drainage rate of 5.6 mm d⁻¹ and 2.14 kgha⁻¹ in 55 m spacing with a drainage rate of 3.5 mm d⁻¹. The rice yield was 6.5 Mg ha⁻¹ in15 m drain spacing where no ammonium losses throughsubsurface drainage effluent occurred. The rice yieldsunder 35 and 55 m drain spacings were 1.9 and 1.8 Mgha⁻¹, respectively. The poor yield was due tosignificant loss of ammonium form of nitrogen throughthe drainage effluent and lesser availability of totalnitrogen to the plants. The plant uptake of nitrogen in the unreclaimed area with 55 m spacing was half ofthat in the reclaimed area with 15 m spacing.

The effect of soil treatment with brominal (a herbicide) and theinsecticide selecron (the equivalent field rates and five-fold) on population counts of bacteria, actinomycetes and celluloyticfungi in soil was tested throughout 10 weeks incubation at28 °C. Also, tested their effect on four soil enzymes:cellulase, acid phosphatase, alkaline phosphatase andarylsulphatase. Bacterial and actinomycetes populations in soiltreated with the two pesticides were promoted at fieldapplication rates and inhibited at higher levels. The twopesticides significantly decreased the total number ofcellulolytic fungi and most fungal species after most incubationperiods either by one or the two used levels but the effect ofselecron was more pronounced.Cellulase activity in soil treated with brominal and selecronwas inhibited after most incubation periods. The effect of soiltreatment with the two pesticides on acid phosphatase waspromotive at field application rates after some incubationperiods but the enzyme activity was delayed at the higherapplication doses. Alkaline phosphatase activity in treated soilwas accelerated with both pesticides even at the higherapplication rates, suggesting a direct role of alkaline soil pHin increasing resistance of alkaline phosphatase to pesticides.The effect of soil treatment with pesticides on arylsulphataseactivity fluctuated between promotion and inhibition, butinhibition was predominant.

The cement industry has been one of the major sources of air pollution in the past and the Turkish Air Quality Protection Regulation has issued limits also to trace elementemissions to minimise the polluting effects of this industrialsector. In the present study, dust samples were obtained isokinetically from 18 main stacks of 10 cement plants locatedin different geographical areas of Turkey. The samples were analysed for trace elements Hg, Cd, Cr, Pb, Ni, Se, Te, TI, V, Sb, Ba, Zn, Co, Sr, Cu, Bi, Mo, Be, and As. The results are presented both as concentration in the dust samples as well as emissions per unit production, and concentration inthe stack gas. The trace element emissions of the main stacksagree to great extent with the values given in the literature. On the other hand, the trace element emissions of the plants considered are well below the limits set in the Turkish Air Quality Protection Regulation.