A 2-yr (1997–1998) survey aiming at the establishment of national data bases concerning the quality of surface waters has been conducted in the major river systems of Macedonia, N. Greece. This paper presents the physicochemical parameters(pH, conductivity, total suspended solids, temperature and DO),the organic pollution parameters (BOD₅, COD) and the major N and P species (NO₃ ⁻, NO₂ ⁻,NH₄ ⁺,organic N, orthophosphates and total P) determined at 25 sampling sites located on main rivers, tributaries, streams andditches that drain the major rural, agricultural, urban and industrial areas of N. Greece. Use of multivariate statistics is also made to identify the principal factors which influencethe chemistry of the water in individual river systems.The eutrophication status of the examined systems was evaluatedby means of N/P ratios. Mean N/P ratios showed large variationsamong sampling sites ranging from potential N- to P-limitationconditions. N/P ratios at particular sampling sites showed also great temporal variability thus suggesting temporary states of N- or P- limitation. Most frequently, highest ratio values wereobserved during winter and early spring. Comparisons are made between data from this study region and literature on rivers elsewhere.

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.

Laboratory and field experiments werecarried out with 2,4-D herbicide(2,4-Dichlorophenoxyacetic acid) to evaluate itstransformation and migration in the coastal waterprotection zones of the Oka river, Russia. In thefirst laboratory experiment, the transformation of2,4-D was studied in various soil samples from coastalslopes (1–0°) of 480 m length soil-geochemicalcatena on the right side of the Oka river incomparison with watershed and floodplain soils. Thetransformation of 2,4-D was the lowest in soil sampleswith minimal pH values and was independent of eitherslope values or vicinity to the Oka river channel.Using indirect estimates, the surface runoff potentialwas calculated for this herbicide. In the second fieldexperiment, the vertical migration and transformationof 2,4-D was carried out in soddy sand soil (EutricArenosol) placed in the left side of the Oka river(0-100 cm) under `soft' (40 mm 2 hr⁻¹) and `hard'(40 mm 15 min⁻¹) irrigation regimes. Furthermore, thetransformation of this herbicide was studied in 0–20and 40–50 cm soil layers under various temperature andmoisture regimes. After 1 day of irrigation, the mainherbicide quantity was found in the 0–30 cm layerunder both irrigation regimes. The transformation ofthe herbicide was faster in the surface, 0–20 cmlayer, than in the deeper, 40–50 cm layer.

Air monitoring stations were set up at 2 sites in the southern hemisphere — Moody Brook, Falkland Islands (51° 25′ S, 57° 56′W) and Halley, Research Station, Antarctica (75° 35′ S, 26° 30′ W). PCBs were monitored at the stations throughout 1999. Highest concentrations were observed when temperatures were greater. In general, concentrations were greater at Moody Brook than at Halley, although the difference in concentrations between sites was less for more chlorinated congeners. Air concentrations at both sites were compared with samples collected nearby over-water. Over water air concentrations were found to be greater than over land air concentrations. Concentrations were also compared with literature data for air concentrations at a remote site in the Canadian Arctic. Atmospheric concentrations of tri-chlorinated biphenyls were found to be approximately double those reported for Ellesmere Island in the Canadian Arctic, whilst concentrations in samples from Antarctica were very similar to those found in the high Arctic. Most other PCBs were a factor of 2–4 greater in the Canadian Arctic.