Environ. Sci. Technol. 1997, 31, 96-104
Distribution of Halogenated Organic Material in Sediments from Anthropogenic and Natural Sources in the Gulf of Finland Catchment Area H A R R I T . K A N K A A N P A¨ A¨ * A N D M A R J O A . L A U R EÄ N Finnish Institute of Marine Research, P.O. Box 33, FIN-00931 Helsinki, Finland RIITTA J. SAARES Finnish Environment Institute, Laboratory, Hakuninmaantie 4-6, FIN-00430 Helsinki, Finland LAURI V. HEITTO Water Protection Association of the River Kymi, Tapiontie 2A, FIN-45160 Kouvola, Finland U ¨ LO K. SUURSAAR Estonian Marine Institute, Paldiski Road 1, EE0001 Tallinn, Estonia
Organochlorine compounds present in effluents from the pulp and paper industry are regarded as a potent threat to the environment. Total organohalogen concentrations are commonly measured in sediment as extractable organic halogen (EOX). Spacial and vertical levels of EOX were determined in areas likely to be affected by organochlorine pollution in Lake Saimaa, along the Kymi River, and around the Gulf of Finland. High levels of EOX were found in samples from southern Lake Saimaa and the Kymi River. Spacial EOX distribution indicated that there is transport of organochlorines from the Kymi River to the eastern Gulf of Finland, and EOX results from the Kotka area showed that substantial, widespread, organochlorine pollution persists 30 km off the coast. Sediments from Vyborg Bay (Russia) and from Tallinn Bay and Ihasalu Bay (Estonia) contained low amounts of EOX. Results from 73 stations indicated that pollution from chlorine bleaching and municipal water chlorination remains localized. Vertical EOX distributions in sediment samples from the whole Gulf of Finland and results from a sediment trap experiment in the open Gulf suggest that naturally produced halogenated compounds are contributing to surface sediment concentrations and, furthermore, far exceed the anthropogenic contribution.
Introduction The pulp and paper industry is one of the main producers of the chlorinated compounds found in the Baltic Sea, producing more than 70% (1) of the total organohalogen load. Other sources of anthropogenic organohalogens are industrial wastes, agriculture, and everyday use of chlorine chemicals (bleaching and cleaning agents, etc.), but there are no reliable * Corresponding author telephone: + 358 9 613 941; fax: + 358 9 613 944 94; e-mail:
[email protected].
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figures for the total load. More than 50% of the total organochlorine input from pulp mills since the early 1940s now reside in the basins of the Baltic Sea. Since about 80% of this bulk is bound in the bottom sediments, basin sediments represent a key matrix for the study of organohalogens in the Baltic marine environment (2). In the Bothnian Sea and the Baltic Proper, the total quantities and the distribution of halogenated pollutants have been estimated (3-5). In the Bothnian Sea, pollution from the pulp and paper industry is localized in the vicinity of the point sources (6). Information from the Gulf of Finland has been scarce. Our earlier work has reported substantial levels of organochlorines from the pulp and paper industry in sediments around the town of Kotka (7), but an overall picture of the distribution of these compounds for the whole Gulf of Finland has not been described. The parameters most commonly used to describe total concentrations of organohalogens in water and sediment are the sum parameters of adsorbable organic halogen (AOX) and extractable organic halogen (EOX), which are usually determined by microcoulometric detection. These do not provide information on the chemical character of the constituents measured, but they do provide a practical means for estimating pollution from chlorination processes. Parameters closely related to EOX are extractable organic chlorine (EOCl), extractable organic bromine (EOBr), and extractable organic iodine (EOI), which are analyzed by neutron activation analysis (NAA), which permits the determination of specific halogens. The method of extraction varies from laboratory to laboratory, and this complicates comparison of EOX results from different laboratories. Microcoulometric cells are more sensitive to chlorine than bromine, so that, theoretically, EOX ≈ EOCl + 0.3 EOBr. The proportion of EOBr in the total EOX pool in sediments has been observed to increase toward the southern Baltic (8), which suggests that the natural production of brominated compounds by algae may be significant. Chlorophenolic compounds (chlorophenols, chloroguaiacols, and chlorocatechols) are another indicator group for estimating organohalogen pollution from the pulp and paper industry, wood preservation, municipal water chlorination, and combustion (9, 10). Although the effluents from the pulp and paper industry have been until now regarded as the main source of organohalogens in the Baltic Sea, toxicologically the effects of bleaching effluents in both water and sediment remain controversial (e.g., ref 11). There is evidence that they have a harmful effect on the behavior and metabolism of marine organisms (12-16). Description of Study Area. The Gulf of Finland (area 30 000 km2) is a shallow (average depth 37 m), estuarine arm of the Baltic Sea (Figure 1). The water-body of the Gulf (1100 km3) is very small in relation to the total riverine inflow (100125 km3 a-1) from a great catchment area (420 000 km2). These facts mean that the ecological state of the Gulf is naturally vulnerable and easily exacerbated by pollution from the agriculture, industry, and other activities of the nearly 10 million people that live in the area. Sedimentation rates in the Gulf of Finland are frequently high (up to 1 cm a-1) in comparison to most other parts of the Baltic Sea (17), and the Gulf is well-suited to sediment studies. The topography of the seabed is broken by innumerable small islands along the coastline, and Gulf of Finland sediments have a mosaic distribution. In the northern part of the Gulf, the basins with recent, soft sediments are small compared to the basins found in the middle and southern part, where they may reach a depth of 123 m. In general, active sediment basins are separated from each other by thresholds of bedrock, till, or
S0013-936X(95)00904-7 CCC: $14.00
1996 American Chemical Society
FIGURE 1. Location of study area. limnoglacial clay. Postglacial sediments may be 10-15 m thick in some places. The Bights of Koporskaya and Luzhskaya are located on the south coast of the eastern Gulf of Finland in Russia. Our earlier data (18) indicated that these areas were unlikely to show pollution from man-made organochlorine compounds, and since this was later shown to be the case, the KoporskayaLuzhskaya area became our reference area. For similar reasons, station S5 (Lake Saimaa) was also selected as a reference location. Station GF2, located in the middle of the Gulf of Finland, was selected for monitoring temporal change in the deposition of organohalogen material. The Kymi River, the largest river on the Finnish side (mean discharge 298 m3 s-1), flows into the eastern Gulf through the town of Kotka, dividing into two branches forming just before the town. The river-bed consists mainly of transportation bottoms, which vary from soft anaerobic mud to gravel depending on the gradient of the bottom and the current velocity. The Saimaa Lake System forms the largest body of freshwater in Finland (4400 km2). The system drains through the Vuoksa River (mean discharge 596 m3 s-1) into Lake Ladoga (in Russia) and, to a much lesser extent, through the Saimaa Canal (mean discharge 2 m3 s-1) into the Bay of Vyborg. The sediments of the southern part of Lake Saimaa, the subject of this study, are characterized by net deposition of mud. Sources of Pollution. With regard to pollution from Finnish sources, two pulp mills on the Kymi River are responsible for most of the bleaching effluent entering the Gulf of Finland, in the town of Kuusankoski 70 km upstream, and in the town of Kotka near the estuary. At the Kuusankoski mill, chlorination was introduced at the turn of the century. In 1989, the introduction of a secondary-activated sludge plant produced a marked reduction in the AOX load. The Kuusankoski mill began producing elemental chlorine-free (ECF) pulp (bleached with ClO2 and O2) in 1992. Pulp production in 1994 was 436 000 t with a total AOX load of 0.4 kg/t of pulp.
At the Kotka mill, the situation was similar. Chlorination began in the 1950s, and the use of elemental chlorine was terminated in 1992. Today the Kotka mill produces both ECF (bleached with ClO2 and O2) and total chlorine-free (TCF) pulp. A secondary-activated sludge plant came on-line in May 1995. Pulp production in 1994 was 306 000 tons with a total AOX load of 1.0 kg/t of pulp. Three pulp mills discharge their wastewaters into southern Lake Saimaa. In 1994 the Lappeenranta mill was producing 435 000 t of ECF (ClO2 and O2) and TCF pulp with a total AOX load of 0.25 kg/t of pulp. In the same year, the Joutseno mill produced 320 000 t of ECF pulp (ClO2 and O2; 0.47 kg of AOX/t of pulp), and the Imatra mill produced 564 000 t of ECF pulp (0.51 kg of AOX/t of pulp). All three pulp mills have secondaryactivated sludge plants. The Saimaa Canal, connecting Lake Saimaa to Vyborg Bay, may also play a small part in transporting bleaching effluents to the Gulf of Finland. In the town of Sovetskiy on the Bay of Vyborg, there is a paper mill that does not produce bleached pulp, but chlorinated, municipal wastewater is discharged into the bay together with industrial effluents. Sovetskiy is probably a source of organochlorine pollution. Our previous results from the Neva Estuary have not revealed pulp industry pollution from the St. Petersburg Region (Lake Onega-Lake LadogaNeva River water system) (6). On the south side of the Gulf of Finland, there is a pulp and paper factory in the city of Tallinn (Tallinn Bay), and another in the town of Kehra (27 km upstream from where the Ja¨gala River enters Ihasalu Bay), but according to our information, neither has produced bleached pulp. The Tallinn mill had an annual production of 60 000 t of sulfite cellulose, and the Kehra millhad about 50 000 t of sulfate cellulose. Until 1989, waste from the Tallinn mill was discharged, untreated, to the southern part of Tallinn Bay, one of the most polluted zones on the Estonian coastline in those days. Following Estonian independence, these mills were closed in 1993. Both mills were reported to have not used chlorine chemicals, but this had to be checked. In Tallin, the chlorination of drinking water is using 500 t of chlorine annually and may be a source of organochlorines. The objectives of the present work were (i) to obtain a comprehensive picture of total organohalogen concentrations in sediments in areas potentially threatened by organohalogen pollution and (ii) to estimate the contribution of anthropogenic sources and natural production to the organohalogen pool in Gulf of Finland sediments.
Materials and Methods Sampling, Storage, and Pretreatment of Samples. Recent sediment deposits were selected with the help of Quaternary deposit maps for the Kotka area (19) and, in the rest of the study area, with information from Russian, Estonian, and Finnish scientists and other authorities. Sediment sampling was performed during cruises with the Finnish R/V Aranda and R/V Muikku and the Russian R/V Persey, between June 1993 and September 1995. For the study area and location of pollution point sources, refer to Figures 1-3. Settling particulate material was collected using a 1.33 m L conical, automatic sediment trap (Technicap P.P.S. 5/2, France) equipped with 24 250-mL receiving cups made of polypropylene. The trap was placed at a depth of 64 m (20 m above bottom) at station GF2 (59°50.27′ N, 25°51.58′ E). The time of operation was from May 17 to September 22, 1995. Each cup, prefilled with 5% (v/v) formalin solution (Merck, p.a.) containing 10 g/L NaCl (Merck, suprapur), was set to collect for exactly 3 days. Bottom sediment was sampled at the same location, both before and during the trap sampling operation (April 27, May 17, July 7, and August 8, 1995). Bottom sediments were sampled using gravity corers with internal diameters of 50 (20), 80, and 90 mm. Sediment cores were sectioned into 1-cm subsamples except in the Lake Saimaa and Kymi River areas, where subsamples were
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FIGURE 2. Spacial distribution of EOX (µg of Cl/g dw; circle radius, µg of Cl/g of C; circle color) illustrating sediment layers 0-1 cm (Gulf of Finland), 0-2 cm (Lake Saimaa), and 0-3 cm (Kymi River).
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FIGURE 3. Spacial distribution of core EOX averages (µg of Cl/g dw; circle radius, µg of Cl/g of C; circle color) from layers 0-core bottom and classification of Gulf of Finland cores. White circles: no TOC result. Subtype I: nonpolluted cores. Subtype II: polluted cores. The total length of the cores from the Gulf of Finland were 15 cm (K3, K9, K12-13, K15, K18, and K22-K24), 10 cm (J5, K16, K19-K20, K22, K27, T2, and V5), 8 cm (K2 and L2), 7 cm (K21), 5 cm (GF2, J3, J6, J8, K1, K4-K8, K11, K14, K17, K26, T1, T3-T4, and V3-V4), 4 cm (J7, V12), 3 cm (J1-J2, J4, K10, V1-V2, V6-V11, and T5-T7) and 2 cm (KP1-KP3, L1, and L3-L4). Samples from the Kymi River and Lake Saimaa were 6 cm long.
sectioned at 2 and 3 cm, respectively. Sediment samples from the whole study area were frozen (-20 °C), lyophilized, weighed, and homogenized after dry-weight measurement. At station GF2, only the surface sediment (0-1 cm) was collected for temporal studies. For other core lengths refer to Figure 3. Bottom water samples, from just above the core surface, were taken (stations V1-4, V7, V12, T4-T5, and T7) in 0.5-L plastic bottles and refrigerated. Validation of the EOX Method. To ensure the reliability of results, the EOX method for analyzing sediments was validated. Validation included determining the detection limit (DL) (21) as well as linearity, repeatability, and reproducibility and also including an interlaboratory comparison test. The limit of detection was calculated using the formula DL ) 2 x2 × t0.05 × sw, where t0.05 is the tabulated value of the Student’s t-test (single sided) at 95% probability and sw is the within-batch standard deviation of duplicated blank samples (cyclohexane-isopropanol) determined during a period of 7 days. Linearity was measured with standard solutions of p-chlorophenol, injected over a range of 2-35 µg of Cl/ injection. The injection repeatability was measured by injecting four different standard solutions and one extract of a contaminated sample 10 times consecutively. Injection reproducibility was measured by injecting three different standard solutions per day over a period of 9 days. The repeatability of the EOX method was measured using sediment samples from stations KY2, KY3, and S2 and by conducting from one to four EOX measurements per sample per day for 3 days. EOX method reproducibility was measured over a period of 10 days using sample KY3. In the interlaboratory comparison test, made by the Finnish Environment Institute and the Finnish Institute of Marine Research, five different sediment samples (stations S1-S5) were measured for EOX in duplicate or triplicate, in both laboratories, and the results were processed with the Student’s t-test. Extraction of EOX from Sediment Samples. The method used was a modification of a procedure by Martinsen et al. (22) and described by Kankaanpa¨a¨ and Tissari (18). In brief, 0.2-10 g of pretreated sediment sample was weighed, and the organohalogen compounds were extracted by sonication (2 h) in 75 mL of cyclohexane-isopropanol (4:1, v/v), followed by strong agitation in a vertical rotator (16 h). Sediment and solution were separated by centrifuging. Supernatants were washed twice with 25 mL of 0.2 M KNO3 (pH 2) solution to remove inorganic chloride. The extracts were concentrated to 2-5 mL with a rotary evaporator and then to 0.5-1.0 mL under a gentle nitrogen flow and finally were centrifuged to remove any remaining precipitate. All reagents used in this and all other procedures were p.a. grade and all solvents were HPLC grade. Preparation of Bottom Water Samples for AOX Analysis. AOX measurements were made according to standard ISO 9562 (23). A sample of 100 mL of bottom water was adjusted to pH 2 with concentrated HNO3, to which was added 5 mL of 0.2 M KNO3 solution and 100 mg of activated carbon. The mixture was agitated for at least 16 h and then filtered onto a polycarbonate filter. The filter and activated carbon were washed twice with 20 mL of 0.01 M KNO3 (pH 2) solution and twice with 20 mL of deionized water. Analysis of EOX and AOX. For each EOX analysis, three 50-100-µL aliquots of extract were injected into either a Euroglas ECS 1000 or Euroglas ECS 2000 analyzer with combustion in O2 at 850 °C. For each bottom water AOX analysis, at least two separate analyses were made by combusting at 1000 °C the filter of the subsample used. The resulting halides were titrated microcoulometrically and calculated as chlorine equivalents (µg of Cl/g or µg of Cl/L). EOX results from sediments were normalized to dry weight (dw) and, in order to compensate for minerogenic differences in sediments, also to total organic carbon (TOC). AOX from water samples was normalized only to volume. Pentachlo-
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rophenol was used as a control to ensure the accuracy and precision of the analyses. TOC Analysis of Sediment Samples. Two or three weighed subsamples of each pretreated sediment sample were combusted in pure oxygen at 900-950 °C using UNICARBO VI or Shimadzu TOC-5000 equipment. Total organic carbon was measured as CO2. Oxalic acid or glucose was used as a standard. Analysis of Free and Bound Chlorophenolics. Briefly, sediments from the trap and surface sediment from station GF2 were extracted with 6 M NaOH and back-extracted in ether. The chlorophenolics were acetylated with acetic anhydride and extracted in hexane. Quantitative analyses were made using a GC/ECD system equipped with a capillary column. The concentration of chlorophenols (PCP), chloroguaiacols (PCG), and chlorocatechols (PCC) was measured, and their total concentration (∑PCP) in sediments was calculated. All of these measurements were carried out at the National Public Health Institute, Kuopio, Finland.
Results and Discussion Sediment Characteristics. All the sediments from Lake Saimaa consisted of mud with oxidized surface. Sediments from the Kymi River contained clayey mud with industrial fibers and oxidized surface, except for stations KY4 and KY5, which also contained some gravel and sand. Industrial fibers were also common in cores from the Kotka area. In some cores, colonies of Beggiatoa bacteria were found. In the Gulf of Finland, the sediments sampled consisted mainly of recent mud with oxidized surface. In some cores, tunnels and holes were observed, presumably made by benthic animals. In general, the sediments taken near the Estonian coast contained larger amounts of clay, reflected in high, surface dry weight and low, organic material content, particularly at stations J8, T4, and T7. Clayey sediments were found also at stations K8, K14, K17, and K18. The material collected with the sediment trap consisted mainly of planktonic material; the most abundant species were Achantes taeniata (April 27May 29, less during June 25-July 7), Thalassosira baltica baltica (April 27-May 15, July 28-August 8), Skeletonema costatum (before July 16), Chaetoceros wighamii (June 10July 7), and Aphanizomenon sp. (July 16-28). EOX Validation. The results of validation and the interlaboratory comparison test indicated that the EOX method has good repeatability and reproducibility. The interlaboratory comparison test showed that the results of the two laboratories differed from each other by less than 8% with samples containing over 50 µg of Cl/g. In samples containing less than 2 µg of Cl/g of EOX, the RSD was up to 25%. With a confidence level of 95%, results did not differ significantly between the two laboratories. For results refer to Table 1. Spacial Distributions in the Kotka-Kymi River Area. The spacial, surface (0-1 cm) EOX distribution in the Kotka area (6-120 µg of Cl/g; 160-920 µg of Cl/g of C; Figure 2) indicated that pollution from the pulp mills is spreading at least 30 km from Kotka to the Gulf of Finland, to station K23, where EOX levels were still 17 µg of Cl/g (160 µg of Cl/g of C). Closer to Kotka, the surface EOX concentrations reached 50-120 µg of Cl/g (500-920 µg of Cl/g of C). The elevated EOX levels found near Kotka were of the same order as those found in areas affected by pulp mill discharges in the Gulf of Bothnia and the Gulf of Finland (5, 7). Figure 3 illustrates the EOX averages for the whole core (0-core bottom). Surface sediments (0-3 cm) from the Kymi River contained high amounts of EOX ( 95 RSD < 6%, R% > 92 5% < RSD < 17% RSD < 7% RSD < 8%, when X > 50 µg of Cl/g; RSD < 25%, when X = 2 µg of Cl/g; r ) 0.982
a Sediment dry weight. b Final volume of extract. c Theoretical chlorine concentration. d Coefficient of correlation. e Number of parallel measurements. Relative standard deviation. g Recovery percentage. h Mean EOX concentration in sediment. Injection volume in EOX method was 100 µL.
KY5 are affected by mill effluents. Surface organohalogen levels were observed to increase from station KY1 to station KY3 and to decrease going downstream to station KY7. The trend suggests that, while most of the EOX material transported by the river is deposited before station KY7, at least some EOX-containing material ends up in the Bay of Ahvenkoski, because at stations K24 and K26 the surface EOX was up to 28 µg of Cl/g (500 µg of Cl/g of C) and 38 µg of Cl/g (640 µg of Cl/g of C), respectively. This transport may extend as far as station K27 (18 µg of Cl/g; 250 µg of Cl/g of C), although effluents from the Kotka mill may also be transported to K27 by the overall east-west flow in this part of the Gulf. Spacial Distributions in the Russian and Estonian Sea Areas. In general, EOX concentrations in the surface layer in the Vyborg Bay area were low (3-10 µg of Cl/g; 31130 µg of Cl/g of C, Figure 2), being in the same order as the surface concentrations in the Luzhskaya-Koporskaya reference area (6-13 µg of Cl/g; 82-190 µg of Cl/g of C). These observations indicated that (i) the industrial and municipal effluents from Sovetskiy are not polluting the sediments (3-5 µg of Cl/g and 30-60 µg of Cl/g of C at stations V4 and V3, respectively) and that (ii) transport of EOX material from Lake Saimaa to Vyborg Bay is negligible. At station V4, however, close to Sovetskiy, 19 µg of Cl/g (220 µg of Cl/g of C) of EOX was found in the 3-4-cm sediment layer, indicating that chlorinated compounds have been deposited in the past. AOX levels in the bottom water at the Sovetskiy stations (V3 and V4) were rather high (180-240 µg of Cl/L) compared with values from the other Vyborg Bay stations (26-55 µg of Cl/L). This observation suggests that compounds formed during the chlorination of municipal wastewater are not deposited immediately. All surface samples from Ihasalu Bay in Estonia contained very low amounts of EOX (1-4 µg of Cl/g; 40-120 µg of Cl/g of C). Deeper sediment layers were also not polluted, confirming information that chlorine chemicals were not used at the Kehra mill. There was no clear indication of pulp mill pollution in Tallinn Bay either, but surface EOX levels were somewhat higher (2-17 µg of Cl/g; 110-310 µg of Cl/g of C) than in the Ihasalu and Vyborg Bays. The slightly elevated EOX levels in surface sediments at stations T1-T3 and at T7 (Figure 2) may be a result of the chlorination of Tallinn’s municipal water supply. Despite this, bottom water AOX in Tallinn Bay was low (27-74 µg of Cl/L) and of the same magnitude as in Vyborg Bay. In the relatively open and deep waters of Tallinn Bay, dispersion and dilution of chlorinated compounds over the sea-bed is most likely enhanced by the large size of the sedimentation basins. Whereas, in contrast, chlorinated material is probably concentrated by the smaller sedimentation basins of the northern Gulf. Because the most recent sediment layers contained only slightly elevated quantities of EOX, it is possible to postulate that sedimentation may be scavenging chlorinated material from the watermass. For average EOX in the deeper sediment layers, refer to Figure 3. Spacial Distributions in Southern Lake Saimaa. Observed surface (0-2 cm) EOX concentrations varied from 64
to 150 µg of Cl/g (560-1340 µg of Cl/g of C, Figure 2). The highest EOX concentrations were measured at stations S1 (130 µg of Cl/g) and S3 (150 µg of Cl/g). Compared with the reference sample, station S5 (2 µg of Cl/g; 23 µg of Cl/g of C), these levels are relatively high. Results indicate that organochlorines are still being emitted by the Saimaa pulp mills and may be causing pollution over a wide area of the lake. Transport of organochlorines through the Vuoksa River to Lake Ladoga may occur. Results indicate that transport to Vyborg Bay through the Saimaa Canal is negligible. Comparison with Earlier Data. It is difficult to compare directly our EOX results with earlier data from other parts of the Baltic Sea, because most previous results are based on the use of EOCl, EOBr, and EOI parameters (e.g., refs 6 and 8), which require different extraction, normalization, and halogen detection. With regard to the earlier results, in general, levels of EOX in the Gulf of Finland show a similar decrease with increasing distance from source to those observed in the Gulf of Bothnia, where EOCl levels (near source) of >200 µg of Cl/g loss of ignition (LOI) decreased to about 10 µg of Cl/g LOI in the open parts of the Gulf of Bothnia (6). This distance-dependent decrease in EOX can be observed in the Kotka area, but here the complex bottom topography and the presence of local active basins affect the distribution pattern, e.g., station K17 shows a low sedimentation rate and rather low EOX and station K18 shows a higher sedimentation rate and higher EOX. Implications of Vertical EOX Distribution in the Gulf of Finland. Vertical EOX profiles from the Gulf of Finland can be divided in two groups: (I) nonpolluted cores, where a steady, low EOX level in deeper layers shows a sudden increase near the core top and (II) polluted cores, in which an abrupt increase near the core top is frequently more pronounced. In each and every core, the vertical EOX profiles obtained after normalization to dw and TOC reflected each other closely. Because sediment samples from the Gulf of Finland were sectioned at 1 cm, changes in vertical EOX could be clearly observed (Figure 4). For core classification refer to Figure 3. The vertical EOX profiles for the nonpolluted cores (type I) shown in Figure 4 may be explained by different primary production and different sedimentation of natural organic halogen material in different areas. In eutrophied areas (e.g., in coastal zones), increased nutrient levels from fertilizers may stimulate algal production, leading to high sedimentation rates and high EOX levels in surface sediments. Intensive algal production may explain the rather high EOX concentrations and the vertical distribution of between 2 and 4 µg of Cl/g (>3 cm) to 5-10 µg of Cl/g (0-3 cm) found in cores from the Vyborg Bay, from the Koporskaya-Luzhskaya area, and from station T6. In other cores of type I, EOX levels stay relatively constant at 0.2-3 µg of Cl/g below 3 cm, but may rise by 1-3 µg of Cl/g above 3 cm (e.g., J5). In this case, EOX distribution may be caused by less intense natural production and lower sedimentation rates. Cores exhibiting these lower EOX levels were found in the Tallinn-Ihasalu area and also at station
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FIGURE 4. Examples of vertical EOX (µg of Cl/g of dw) distribution in cores. Results for individual stations are linked by spline curves. Subtype I: nonpolluted cores. Subtype II: polluted cores. Error bars (RSD of injections) are not shown when smaller than points on the curve. K10. In all cases, decreasing EOX levels toward core bottom can be explained by remineralization of organic material. In the polluted Kotka area (cores of type II), we observe changes in historical input, and it is possible to distinguish between increased, constant, and decreased deposition of EOX. The stations exhibiting constant anthropogenic input (within 15-40 µg of Cl/g throughout the core) were K1, K6, K11, K13, and K26, and the stations exhibiting decreased input (from 20-90 to 12-50 µg of Cl/g) were K2, K4, K5, K7, K8, K12, and K24 (Figure 4). The results for these stations, near the mouth of the Kymi River, may be explained partly by reduced loading from the Kuusankoski mill. Cores from the outer Kotka area showed an increase in EOX content. At stations K14, K16, K19, and K27 the deepest part of the core contains 3-20 µg of Cl/g and EOX increases to 13-27 µg of Cl/g in the top of core. Why increased EOX deposition should occur in the outer Kotka area is not sure but it may be related to tranquil bottom conditions that permit final sedimentation of EOX material and also to inadequate wastewater purification at the Kotka mill. Cores from stations K3, K9, K15, K17, K18, and K20-K23 are characterized by slightly elevated EOX (1-30 µg of Cl/g) with an abrupt increase near core top (up to 116 µg of Cl/g at K15). This distribution may be caused by (i) low sedimentation rate combined with recent anthropogenic loading or (ii) polluted sediment redeposition, e.g., at station K17 where EOX increases from 0.4-2.0 (1-5 cm) to 35 µg of Cl/g at the surface. A less pronounced historical change in EOX deposition can be observed in cores from stations T1-T3 and T7 in the Estonian area, where surface layers (0-2 cm) contain 5-17 µg of Cl/g (100-300 µg of Cl/g of C) EOX and deeper layers contain 1-3 µg of Cl/g (30-100 µg of Cl/g of C). Vertical EOX Distributions in the Kymi River and Lake Saimaa. Of the Kymi River stations only KY3, exhibiting decreasing EOX toward core top (420-110 µg of Cl/g), could be interpreted satisfactorily. At this station, we assume that organohalogens existed in the 3-6-cm layer until the 1980s
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and that, thereafter, the diminishing surface EOX reflects the introduction of more effective effluent purification at the Kuusankoski mill. Also, higher results in the 3-6-cm layer could be explained by surface sediment erosion. Infact, decreased input from the mills was observed at all Kymi River stations, although not as clearly as at station KY3 (Figures 2 and 3). At all polluted Lake Saimaa stations, EOX (Figures 2 and 3) increases toward core top, and at station S3 concentrations were high and constant (140-160 µg of Cl/g; 1290-1360 µg of Cl/g of C) throughout the core. These observations suggest that the deposition of chlorinated material has been increasing. As elsewhere, organohalogen mineralization may also be contributing to the lower EOX in the deeper layers. At station S3, where the EOX concentration was highest, mixing was observed in the surface sediment, and this may partly explain the constancy of EOX distribution. Natural Organohalogen Production in the Gulf of Finland. Surface EOX results from nonpolluted cores agreed well with Gulf of Finland background levels (0.5-6.0 µg of Cl/g) reported earlier (18). The results obtained indicated, however, that the highest background levels reach 8-10 µg of Cl/g (100-150 µg of Cl/g of C) during times of active natural production (algal blooming) and also in areas with relatively high sedimentation rates. Increases in surface EOX, especially in nonpolluted areas, may be caused by the natural production of new, EOX-rich material. Indications that the natural production of EOX-rich material is a significant phenomenon in the marine environment were supported by our data from the nonpolluted areas, which showed that there does exist a correlation between surface EOX concentration and sedimentation rate, although the correlation we found is not very strong (r ) 0.60, excluding the outlier KP2). A further indication of the presence of significant natural EOX production comes from the results of the sediment trap and bottom sediment samples from station GF2. Between May 17 and September 22, total deposition in the trap was 200 g of particulate material and 2160 µg of EOX. The level of total chlorophenolics (∑PCP) in the samples was very small or nondetectable (usually
