Acute and chronic toxicity of lead to rainbow trout salmo gairdneri, in hard and soft water

Lead was found to be highly toxic to rainbow trout in both hard water (hardness 353 mg l⁻¹ as CaCO₃) and soft water (hardness 28 mg l⁻¹. Analytical results differ greatly with methods of analysis when measuring concentrations of lead in the two types of water. This is exemplified in LC50's and maximum acceptable toxicant concentrations (MATC's) obtained when reported as dissolved lead vs total lead added in hard water. Two static bioassays in hard water gave 96-h LC50's of 1.32 and 1.47 mg l⁻¹ dissolved lead vs total lead LC50's of 542 and 471 mg l⁻¹, respectively. In a flow-through bioassay in soft water a 96-h LC50 of 1.17 mg l⁻¹, expressed as either dissolved or total lead, was obtained. From chronic bioassays, MATC's of lead for rainbow trout in hard water were between 18.2 and 31.7 μg l⁻¹ dissolved lead vs 120–360 μg l⁻¹ total lead. In soft water, where exposure to lead was initiated at the eyed egg stage of development, the MATC was between 4.1 and 7.6 μg l⁻¹. With exposure to lead beginning after hatching and swim-up of fry, the MATC was between 7.2 and 14.6 μg l⁻¹. Therefore, fish were more sensitive to the effects of lead when exposed as eggs.     

Toxicity of silver to rainbow trout (Salmo gairdneri)

The mean 96-h LC₅₀'s of silver with rainbow trout were 6.5 μg l⁻¹ and 13.0 μg l⁻¹ in soft water (approximately 26 mg l⁻¹ hardness as CaCO₃) and hard water (350 mg l⁻¹ hardness as CaCO₃), respectively. The long-term, “no effect” concentration for silver, added to the water as silver nitrate, was between 0.09 and 0.17 μg l⁻¹ after 18 months exposure in soft water. The “no effect” concentration is that concentration range which defines no observed effect. Based on mortalities different from the control, no mortalities attributable to silver occurred at 0.09 μg Ag l⁻¹, whereas 17.2% mortality occurred to fish exposed to 0.17 μg ll⁻¹. The “no effect” concentration does not reflect possible effects of silver on spawning behavior or reproduction, since female rainbow trout will not generally reach sexual maturity before 3 yr. At silver concentrations of 0.17 μg l⁻¹ or greater, silver caused premature hatching of eggs and reduced growth rate in fry. In one experiment, the eggs were completely hatched within 10 days of exposure; whereas, control eggs completed hatching after 42 days. The prematurely erupted fry were not well developed and frequently died. The growth rate of surviving fry was greatly reduced.     

Addition of NaOH, limestone slurry and finegrained limestone to acidified lake water and the effects on smolts of atlantic salmon (Salmo salar L.)

A neutralization experiment comparing NaOH, limestone slurry and finegrained limestone was performed using smolts of Atlantic salmon as testfish. Smolts were raised on chronically acid Lake Liervatn (pH = 4.9–5.4, conductivity = 55 μ S cm⁻¹, Ca = 1.3 mg l⁻¹, labile Al = 40 μg l⁻¹). As a result testfish were sublethally stressed prior to the experiment, as indicated by low levels of plasma chloride. During the experiment, smolts were held in keepnets in the middle of large plastic enclosures without sediment contact. Rapid changes in pH and Al-speciation were recorded after addition of the neutralizing agents. No mortality of fish occurred during the 3 days exposure. Plasma chloride levels in fish exposed to limestone slurry, limestone and the lowest concentration of NaOH (pH = 5.9) did not differ significantly from levels in fish from the reference group. Fish exposed to the highest concentration of NaOH (pH > 7.45), however, experienced a significant decrease in plasma chloride levels. Increased sublethal stress in treatments with NaOH was presumably caused by the presence of aluminate ions [Al(OH)₄⁻] at high pH and by low concentrations of Ca. The importance of maintaining pH below 7 when using bases with monovalent cations is emphasized. Adding inorganic aluminium to the lake water induced loss of plasma chloride within 48 h at 70 μg labile Al l⁻¹ at pH 5.1 and 1.2 mgCa l⁻¹.     

Effects of aluminum and pH on the early life stages of smallmouth bass (Micropterus dolomieui)

The sensitivity of smallmouth bass Micropterus dolomieui to acidified conditions was examined by exposing recently-hatched fish to pH levels ranging from 5.1 to 7.5 and aluminum concentrations ranging from 32 to 1000 μg l⁻¹. The range of pH and aluminum concentrations included those found in the northern part of the species' range. Acute bioassays (96 h) conducted at a pH of 5.1 and aluminum concentrations 180 μgl⁻¹ resulted in total mortality. The LC₅₀ calculated for this species was 130 μg l⁻¹. At pH values of 6.1 and 7.5, mortality was low ( 20%) regardless of aluminum concentrations. A 30-day chronic toxicity test was conducted at three pH levels (low 5.1, intermediate 5.5–5.7 and high 7.3), each with two aluminum concentrations (approx. 0 and 200 μg l⁻¹). Survival was significantly lower in the test at pH 5.1 with aluminum, and at pH 5.7 with aluminum treatments than in the other treatments. Fish in the pH 5.1 without aluminum treatment had intermediate survival, while fish exposed to pH 5.7 without aluminum, pH 7.3 without aluminum and pH 7.3 with aluminum had high, and similar, survival. Sublethal effects on fish exposed to low pH and aluminum included deformities, reduced activity and abnormal swimming behavior. We conclude that the sensitivity of smallmouth bass to low pH and aluminum concentrations corroborates field investigations linking acidification and aluminum mobilization with depletion of smallmouth bass populations.     

Toxicity of sodium selenite to rainbow trout fry

In a study designed to examine the long-term effects of inorganic selenium (IV) on early life stages of rainbow trout (Salmo gairdneri), survival was significantly reduced at selenium concentrations of 47 and 100 μg l⁻¹ after 90 days of exposure. Length and weight were significantly reduced after 90 days of exposure to 100 μg l⁻¹. Whole-body residues of selenium increased with increasing exposure concentrations but appeared to decline between 30 and 90 days of exposure. Analyses of trout backbone indicated little change in bone development with exposure to selenium (IV) with one exception; calcium concentrations were significantly decreased in fish exposed to 12 μg l⁻¹ of selenium. Results of our study indicates that a recommended safe level of 10 μg l⁻¹ for inorganic selenium would not significantly affect growth and survival of rainbow trout; however, concentrations of selenium near this level can reduce the levels of calcium in the backbones of trout.     

Cardiovascular-respiratory responses of rainbow trout (Salmo gairdneri) during chronic exposure to sublethal concentrations of cadmium

The effects of exposure to 3.6 and 6.4 μg l⁻¹ cadmium for periods up to 178 days on cardiac and ventilatory rates, hematocrit, hemoglobin concentration and erythrocyte adenosine triphosphate concentration in adult rainbow trout, Salmo gairdneri, were investigated. Except for slight transitory responses, 3.6 μg l⁻¹ cadmium had no effect on any of the cardiovascular/respiratory parameters. Significant increases in cardiac and ventilatory rates, blood hematocrit and hemoglobin were observed in fish exposed to 6.4 μg l⁻¹ Cd over the entire exposure period while erythrocyte ATP concentration declined during the last stages of exposure. Further experiments on the responses of fish exposed to 6.4 μg l⁻¹ Cd for 30 days demonstrated an impairment of oxygen transfer across the gill. The results are discussed in terms of possible gill impairment and hyperactivity as toxic responses to cadmium.     

Distribution of halomethanes in potable waters of Kuwait

The distribution of bromine containing trihalomethanes in the water distribution system of Kuwait has been studied. Total halomethanes in the drinking water averaged 25.6 ± 9.1 μg l⁻¹ with a maximum of 50.5 μg l⁻¹. Average concentrations (μg l⁻¹) of individual compounds were: CHBr₃, 13.6 ± 4.6; CHBr₂Cl, 8.8 ± 3.7; CHCl₂Br, 3.3 ± 1.5. Water from roof top storage tanks contained significantly less halomethanes than that from underground reservoirs.     

Studies on the toxicity of copper sulphate to stone loach Noemacheilus barbatulus (L.) in hard water

The toxicity of copper sulphate to Noemacheilus barbatulus was studied for 64 days in a water of total hardness 249 mg l⁻¹ as CaCO₃. The 63-day lc₅₀ was approximately 0.25 mg Cu l⁻¹. Larger fish survived longer, and at concentrations greater than 0.29 mg l⁻¹ fish hid less during daylight. Noemacheilus surviving 0.12 mg Cu l⁻¹ for 64 days shed copper when placed in clean water for 7 days: gill, muscle, eye and vertebrae lost significant amounts of copper during this period. The opportunity to shed copper during a short period when the poison supply to their tank failed, may have allowed fish exposed to 0.49 mg l⁻¹ to live 12 days longer than expected. The sensitivity of Noemacheilus to copper, cadmium and zinc was compared with that of rainbow trout. Salmo gairdneri.     

Investigation of the Folin-Ciocalteau phenol reagent for the determination of polyphenolic substances in natural waters

The methodology associated with the Folin-Ciocalteau phenol reagent was investigated and the performance characteristics of a method using sodium carbonate as the supporting medium were determined. Calibration curves using phenol, tannic acid, or l-tyrosine were linear up to at least 1000 μg l⁻¹. The limit of detection was 6 μg phenol l⁻¹ and the relative standard deviation at 100 μg phenol l⁻¹ was 5.2% and at 1000 μg phenol l⁻¹ was 4.1%. The absorbances obtained with equal amounts of a range of potential standards showed variations when compared with that of phenol: phenol (100%), l-tyrosine (62%), oak gall tannin (58%), tannic acid (48%), chestnut tannin (26%), oak tannin (24%), fulvic acid (5%). The method was applicable to a wide range of monohydric and polyhydric phenolic substances and interferences from inorganic and non-phenolic organic compounds were examined. Interference would be expected above 30 μg S²⁻ l⁻¹, 300 μg Mn(II) l⁻¹, or 400 μg SO₃²⁻ l⁻¹. Concentrations of iron >2 mg l⁻¹ as Fe(II) or Fe(III) formed the insoluble iron(III) hydroxide which increased the absorbance, but centrifugation could be used to remove this source of interference. Other potential sources of intereference (e.g. reducing agents and certain metabolic products) would be expected to have a negligible effect in unpolluted waters. Methods using diazotised sulphanilic acid or 4-aminoantipyrine (4-AAP) were found to be inferior when applied to natural water samples.     

Toxic effects of disyston and furadan on the bimodal pattern of oxygen consumption in the climbing perch, Anabas testudineus (Bloch)

A significant change was noted in the aquatic (vO₂), aerial (VO₂) and total [(v + V)O₂] consumption of Anabas testudineus (Bloch) exposed to 4.0 and 10.5 mg l⁻¹ disyston and 0.56 and 1.56 mg l⁻¹ furadan. After 1 h of exposure to all the concentrations significant decreases were noticed in the (v + V)O₂. Though significant increases were noted in all the measures of respiration after 3 h of exposure in both the pesticides, their effects vary from one exposure period to another. The fish held in 4.0 mg l⁻¹ disyston and 0.56 mg l⁻¹ furadan concentrations resumed normal pattern of bimodal respiration after 120 and 96 h respectively. Further the pattern of changes in (v + V)O₂ closely followed the changes observed in VO₂ rather than vO₂ indicating that the fish held in pesticide medium predominantly relied on aerial respiration. A direct correlation was noticed between the VO₂ consumption and the surfacing frequency of the fish exposed to disyston and furadan. Relatively furadan is more toxic than disyston to Anabas testudineus if their effects on O₂ consumption are taken into consideration.     

Restoration of heavily polluted branches of the Shatt Al-Arab river, Iraq

In view of the desire to improve the water quality of the heavily polluted branches of the Shatt al-Arab River at the City of Basrah, it was proposed to maintain effective flushing as well as contracting sewerage system. The present study was conducted in order to examine the water quality of these branches in an attempt to evaluate the effectiveness of the proposed flushing system. It has been found that their waters contained very low levels of dissolved oxygen and relatively high amounts of both COD and BOD₅. The annual average water quality parameters for Basrah Branches were: dissolved oxygen 3.4 ppm; pH 7.67; hydrogen sulphide 1.4 ppm; ammonia 97 μg-at. N l⁻¹; COD 15.9 mg l⁻¹; BOD₅ 12.7 mg l⁻¹; dissolved silicates 202 μg-at. Si l⁻¹; dissolved reactive phosphate 13.4 μg-at. P-PO₄³⁻ l⁻¹; nitrate 10.4 μg-at. N-NO₃⁻ l⁻¹; nitrite 2.1 μg-at. N-NO₂⁻ l⁻¹ and chlorophyll-α 14.3 mg m⁻³. Based on our calculations, it has been concluded that the proposed system is effective, thus within a flushing cycle all of the above mentioned parameters will become within the acceptable values of the Shatt al-Arab water quality. Moreover, this system has no appreciable effect upon the water quality characteristics of the Shatt al-Arab River due to the fact that it discharges a high volume of water annually. However, It has been recommended to dredge the deposited sludge to a minimum depth of 50 cm.     

Mercury concentrations in fish inhabiting two polluted lakes in Northern Canada

The concentrations of total mercury in the sediments, water and fish of Giauque Lake and Thompson Lake in northern Canada were determined during 1977 and 1978. Both lakes had formerly received mercury-laden industrial discharges, which were terminated in 1968 (Giauque Lake) and 1949 (Thompson Lake). In Giaque Lake, lake trout (Salvelinus namaycusy) contained an average of 3.79 mg kg⁻¹ in their muscle while the average concentrations in northern pike (Esox lucius) and round whitefish (Prosopium cylindraceum) were 1.75 and 1.22 mg kg⁻¹ respectively. About 7% of the lake's bottom contained mercury levels of > 500 μg kg⁻¹ (dry weight) but, in the water, concentrations were always below detectable limits (0.2 μg l⁻¹). In Thompson Lake, mercury levels in northern pike averaged 1.69 mg kg⁻¹, whereas in lake whitefish (Coregonus clupeaformis), the highest recorded value was 0.6 mg kg⁻¹. Although mercury was usually not detectable in the water column, there was heavy contamination of the sediments, with values reaching 1300 μg kg⁻¹. In addition, approximately 15% of the lake bottom contained mercury in excess of 500 μg kg⁻¹. Based on these data, it is concluded that: (1) northern pike are still accumulating mercury from exposed tailings which were deposited in Thompson Lake 30 years ago, and (2) contamination of only a small part of a lake may result in high levels in fish throughout the lake: this is probably due to the movement of fish from contaminated to noncontaminated areas.     

Chlorophenols in surface waters of the Netherlands (1976–1977)

In this paper an analytical method is described for the capillary gas chromatographic determination, after derivatization, of 19 individual chlorophenols in surface water. The minimum detectable amounts are for monochlorophenols 2 μg l⁻¹, for dichlorophenols 0.05 μg l⁻¹, for trichlorophenols 0.02 μg l⁻¹ and for tetra- and pentachlorophenols 0.01 μg l⁻¹. The results of a monitoring program in the river Rhine and other Dutch surface waters with respect to these compounds are presented. The results cover the period January 1976–December 1977. 2,6-Dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol had the highest frequencies of occurrence in the river Rhine and its tributaries. Pentachlorophenol was found in the highest concentrations (up to 11 μg l⁻¹).     

Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations

In this paper, the results of mercury concentrations in two abiotic compartments (river water and suspended particles) and two biotic compartments (fish and human hair) from the upper Madeira rivers of the Bolivian Amazon basin are presented. Because of the local hydrological regimes and a high deposition rate in the plain, due to the presence of a subsidence zone at the bottom of the Andean piedmont, in the dry season, the highest mercury concentrations and fluxes were not found in rivers where mining activities took place (2.25–6.99 ng l⁻¹; and 1.07–8.67 mg Hg d⁻¹ km⁻²), but at the outlet of the Andean basins exploited for their alluvial gold (7.22–8.22 ng l⁻¹; and 9.47–9.52 mg Hg d⁻¹ km⁻²). The total mercury concentrations measured in surface waters of the upper Beni basin varied during the dry season, from 2.24 to 2.57 ng l⁻¹ in the glacial waters of the Zongo river, to 7.00 ng l⁻¹ in the Madeira River at Porto Velho and 9.49–10.86 ng l⁻¹ at its confluence with the Amazon. The results obtained from fish indicate, on one hand, that 86% of the piscivorous fishes collected in the Beni river were contaminated, and, on the other hand, their high mercury concentrations could exceed by almost four times the WHO (1976) safety limit. In the Beni River, the mercury concentrations found in omnivorous and mud-feeding fish ranged from 0.02 to 0.19 μg g⁻¹ (wet wt.), and in piscivorous fish, from 0.33 to 2.30 μg Hg g⁻¹ (wet wt.). The mercury accumulated by carnivorous fishes was mainly present in its organic form; methylmercury represented 73–98% of the total mercury analysed. Eighty persons were studied in the entire Bolivian Amazonian basin. Unlike the gold miners, who are more affected by tropical diseases, such as malaria and yellow fever, the indigenous people living on the banks of the Beni river, present elevated levels of mercury (9.81 μg g⁻¹ on average). We observed an increase in contamination in young children still being breast-fed, confirming that hair mercury concentration in babies was significantly affected by maternal mercury contamination during pregnancy. These results show that the major health impacts caused by mercury affect people who are not working directly in gold mining activities but who have a regular fish diet.     

Acute toxicity and behavioral responses of coho salmon (Oncorhynchus kisutch) and shiner perch (Cymatogaster aggregata) to chlorine in heated sea-water

The acute toxicity and behavioral response to chlorinated and heated sea-water was determined for coho salmon smolts and 1–3 month old shiner perch. LC₅₀'s were determined for 7.5, 15, 30 and 60 min exposure times; 13, 16 and 20°C (Δt = 0, 3, 7°C) temperatures and total residual oxidant (TRO) concentrations ranging from 0.077 to 1.035 mg l⁻¹. The mean 60 min LC₅₀ for shiner perch was significantly reduced (P ≤ 0.05) from 308 μg l⁻¹ TRO at 13°C to 230 μg l⁻¹ TRO at 20°C. The 60 min LC₅₀ for coho salmon decreased from 208 μg l⁻¹ TRO at 13°C to 130 μg l⁻¹ at 20°C. The LC₅₀'s for coho salmon in chlorinated sea-water averaged 55% of those for shiner perch. The relationship between TRO concentration, exposure time, and percent survival in chlorinated sea-water at 13°C is presented for both species.A significant (P ≤ 0.01) avoidance threshold for coho salmon occurred at 2 μg l⁻¹ TRO and was reinforced with increasing temperature. A significant (P ≤ 0.01) avoidance threshold for shiner perch occurred at 175 μg l⁻¹ TRO, while a significant preference (P ≤ 0.05 or 0.01) response at 16°C and 20°C occurred at 10, 25, 50 and 100 μg l⁻¹ TRO. The ecological implications of the toxicity tests and the behavioral responses are discussed.     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

Toxicological effects of dehydroabietic acid (DHAA) on the trout, Salmo gairdneri Richardson, in fresh water

Toxicological and physiological effects of dehydroabietic acid (DHAA), a major poison to fishes in pulp and paper mill effluents, were studied by two experiments with rainbow trout, Salmo gairdneri Richardson: in the first, fish were acutely exposed for 4 days to an average DHAA concentration of 1.2 mg l⁻¹ (Exp. I) and in the second for 30 days to an average of 20 μg DHAA l⁻¹ (Exp. II).Compared to the controls, fish of Exp. I displayed a decreased relative weight of liver, an increased blood haematocrit, and increased haemoglobin as well as plasma protein concentrations. The aspartate aminotransferase activity of heart muscle was significantly elevated, as was also the lactate dehydrogenase (LDH) of white muscle tissue. In the blood plasma, the proportion of muscle type LDH activity was simultaneously increased. UDP-glucuronyl-transferase activities of liver and kidney were strongly decreased. Results suggest an increased and altered use of body energy reserves, decreased plasma volume and impaired liver function.Fish of Exp. II showed an increased relative weight of spleen. In addition, liver and gill LDH shifted towards heart-type. We conclude that 20 μg l⁻¹ is close to the “minimum effective concentration” of DHAA to rainbow trout.     

Toxic effects of hexavalent chromium on brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri)

Exposing brook trout to various concentrations of chromium [Cr(VI)] for up to 22 months (including reproduction) significantly increased alevin mortality at 0.35 mg Cr l⁻¹ and retarded growth of young brook trout at the lowest concentration tested (0.01 mg Cr l⁻¹). Eight month exposures of rainbow trout significantly increased alevin mortality at 0.34 mg Cr l⁻¹ and also retarded growth at the lowest concentration tested (0.10 mg Cr l⁻¹). Exposures of brook trout lasting 22 months showed, however, that growth was only temporarily affected, and therefore, it was not used as an end point to measure the affects of chromium on either species. Reproduction, and embryo hatchability of brook trout were unaffected at Cr(VI) concentrations that affected survival of newly hatched alevins. The maximum acceptable toxicant concentration (MATC) for brook and rainbow trout exposed to Cr(VI) in water with a hardness of 45 mg l⁻¹ (as CaCO₃) and a pH range of 7–8 lies between 0.20 and 0.35 mg Cr l⁻¹. The 96-h lc₅₀ for brook and rainbow trout was 59 and 69 mg Cr l⁻¹, respectively: therefore, the application factor (MATC/96-h lc₅₀) for both species lies between 0.003 and 0.006.     

Mechanism of NTA degradation by a bacterial mutant

Transport of nitrilotriacetic acid (NTA) into the cytoplasm of a bacterial mutant was an active process. The mutant was able to degrade NTA from an initial concentration of 290,000 μg l⁻¹ of NTA to less than 50 μg l⁻¹ in 45 min, representing a rate of 486 μg NTA degraded per hour per mg dry weight of cells. This extremely fast rate of NTA utilization was substantiated by kinetic studies in which a Km of 82 μg l⁻¹ and a V_max of 370 μg h⁻¹ (mg dry weight cells)⁻¹ were found. The maximal temperature for NTA degradation was 50°C. The ability of the mutant to metabolize NTA resided mainly in the cell membrane fraction. Exchange diffusion technique showed that glycine and acetic acid were the metabolic products of NTA degradation. No iminodiacetic acid (IDA), succinate or citrate could be detected.     

Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil)

Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapá State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5–23.4 ng l⁻¹ for rainwater, 16.5–82.7 ng l⁻¹ for throughfall (March–August 1997) and 1.2–6.1 and 4.2–18.8 ng l⁻¹ for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 μg m⁻² year⁻¹ in rainwater and 72 μg m⁻² year⁻¹ in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 μg m⁻² year⁻¹ indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0–10 cm surface layer, which was 36 480 μg m⁻². When the disturbed area of the catchment was included, the stream output was 9.3 μg m⁻², clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 μg m⁻² for the 0–10 cm surface layer.