Organic Micropollutants in Lake Sediments Alfredo Pro ν in i and Silvana Galassi W a t e r R e s e a r c h I n s t i t u t e B r u g h e r i o , I ta ly a n d U n i v e r s i t y of M i l a n , I t a ly

I. Introduction II. Major Classes of Chemicals Associated with

Sediments III. Sources of Pollution IV. Analysis V. Environmental Data

VI. Bioavailability and Environmental Hazard

health both because of remobilization and bioac-cumulation. Chemical analysis is not always ade­quate to cover all the aspects of the organic contamination completely (because of the com­plexities involved), and biological testing is pres­ently being used to assess the hazard of sediment-bound pollutants.

Glossary

Adsorption Surface retention of compounds or ions by a solid or a liquid.

Bioaccumulation Ratio between the concentration in an organism and in the water, air, or food.

Biotic zone Surficial zone of sediment comprising living organisms.

Organic micropollutants Organic compounds mainly of anthropic origin; dangerous for living organisms even at very low concentrations.

Partition coefficient Constant ratio of the solute's concentration in one phase to its concentration in another phase.

ORGANIC MICROPOLLUTANTS, especially those not very soluble in water, tend to accumu­late in sediments. Since lacustrine sediments of the anthropized areas are the storage compartment of these compounds, sediment analysis has been suc­cessfully used to follow their geographical and temporal distribution. Sediment-bound chemicals may represent a risk for aquatic life and human

I. Introduction

Organic compounds of anthropogenic origin are de­livered to lacustrine systems by atmospheric trans­port and deposition, direct discharges, and riverine inputs. When they enter the aquatic environment, their potential for accumulation in sediment is gov­erned by their persistence and hydrophobicity and by the sorptive properties of suspended matter and sediment. Aquatic sediments in lentic systems are the main accumulation site of very persistent and lipophilic pollutants of domestic, urban, industrial and agricultural origin. Organic micropollutants adbsorbed to sediments are usually scarcely bioa-vailable, but sediments from very contaminated areas might represent an important source of pollu­tion for freshwater organisms. Thus, sediment monitoring has been recognized to be very impor­tant both to localize "hot point" pollution areas and to study the pollution of the surrounding aquatic environment.

Sediments are frequently used as indicators of pollution in aquatic environments for a twofold rea­son: first, sediments accumulate very hydrophobic compounds that occur in water at undetectable

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431

432 Organic Micropollutants in Lake Sediments

concentrations; second, sediment analyses allow integration of the fluctuations of the concentrations of the pollutant in water over a certain period of time.

Analysis of surficial sediment provides, there­fore, an average estimate of recent pollution. On the other hand, the analysis of different layers of sediment corresponding to previous deposition pe­riods enables one to reconstruct the historical trend of pollution. Furthermore, since many hydrophobic chemicals are known to partition between water and sediment and this phenomenon can be de­scribed by simple physicochemical models, sedi­ment monitoring can be successfully used to evalu­ate the hazard of some classes of accumulable pollutants for an entire aquatic environment.

II. Major Classes of Chemicals Associated with Sediments

The range of compounds exhibiting substantial ac­cumulation in sediments includes hydrocarbons, chlorinated hydrocarbons, phthalates, and other chemicals with a limited range of bond types. In most cases the predominant bonds are C—C aliphatic, C—C aromatic, C—H, and C—CI al­though other bonds are occasionally present. These compounds are stable to degradation in aquatic en­vironments and are likely to accumulate since this process requires a significant period of time.

The potential for accumulation, that is the con­centration ratio of the compound in sediment and in water at the equilibrium between the two phases, is then ascribable to the lipophilic nature of the compound. Nonpolar compounds with low solu­bility in water are the most lipophilic. Lipophilicity is usually defined by the «-octanol/water partition coefficient, Kov/. Chemicals with a very high accu­mulation potential have log Koxv values ranging be­tween 5 and 7. They represent about 1090 of the approximately 19,000 chemicals currently pro­duced commercially in the United States. Kow can be calculated from water solubility to which it is related through an inverse logarithmic relationship.

Koc, the partition coefficient on soil and sedi­ment, normalized for the carbon fraction content of the sorbent, is also related to water solubility and ATow. Equations that describe such relationships have been experimentally determinated for a num­ber of chemicals and are shown in Table I. The relationships linking Koc with water solubility

hold in the case of the finer fraction of sediment (<60 μπι); a Koc reduction of 50-90% is expected for the coarse fraction.

III. Sources of Pollution

A, Aerial Transport Very persistent and accumulable compounds, such as chlorinated pesticides and polychlorinated bi-phenyls (PCBs), used in huge amounts on a world­wide scale for many years (starting from the 1930s) are by now ubiquitous and appear in most remote areas of the planet. Other compounds, such as po-lycyclic aromatic hydrocarbons (PAHs), are not delivered purposefully into the environment but originate from anthropogenic activities.

Aerial transport is considered to be the major pathway for global contaminants. This is governed by the extent of gas phase/particle phase distribu­tion, since the deposition mechanism and the range of transport depend on it. In the atmosphere, or­ganic micropollutants occur in gaseous aerosol or particulate form. The extent of transport depends on a variety of factors, including particle size, air movement, washout, and vapor pressure. However, most of the environmental xenobiotic burden remains relatively close to the source of contamination, and concentrations decrease ap­proximately logarithmically with distance from the source.

Thus, the majority of organic micropollutants en­tering the aquatic environment are located in lakes, rivers, and coastal waters. Benzo(«)pyrene con­centrations measured by EPA since 1966 in urban air, for example, were higher by one order of mag­nitude than in nonurban areas. Most of PAHs in fact derive from urban and industrial activities.

In the case of pesticides, the atmosphere is contaminated from drifting spray or airborne par-

Table I Relationships between Koc, K{

and Water Solubility

logü: ow = 4.158 - 0.8 log WS (R2 = 0.74) \ogKoc = 3.64 - 0.55 log WS (R2 = 0.71) log Koc = -0 .54 log S + 0.44 (R2 = 0.94) logA:oc = \ogKow - 0.21 (R2 = 1.00) ^ o c

= 0.63 Kow (R2 = 0.96)

Abbreviations: WS, water solubility in ppm, S, water solubility as mole fraction.

Organic Micropollutants in Lake Sediments 493

ticulate matter and through volatilization from agricultural soils. During the sixties, levels of di-chlorodiphenyltrichloroethane (DDT) ranged from 0.1 ng/m 3 of air to 1560 ng/m 3, with higher levels in agricultural areas. Present ambient concentrations in areas where DDT has been severely limited are lower than 0.1 ng/m 3.

Fallout from air and rainfall are considered the main source of pollution by organic micropollu­tants into lakes not subjected to local inputs. The concentrations of pesticides, PCBs, and PAHs in rain and snow has been measured in many studies in different areas of the world. In Table II, some examples of the levels of micropollutants in rain and snow from different geographical areas are given. Other pesticides not included in the table have later been found in rainfall in the United States. Concentrations up to about 6000 ng/1 and 2700 ng/1 were detected for alachlor and me-tolachlor, respectively. Not enough is known about the pathways into and transport in the atmosphere of moderately stable pollutants such as these, but many of them are probably more important than has been realized to date, at least in areas of in­tense agriculture.

Seasonal variations are observed. The higher pesticide levels measured in summer can be related to an increase in usage: the application of lindane (γ-HCH) as a soil pesticide and of herbicides for weed control is mainly done in these areas during spring and at the beginning of summer. It is inter­

esting to note that more persistent pesticides such as lindane and terbutylazine are detected even in winter. On the contrary, the other more degradable herbicides disappear some months after the appli­cation period. In the case of PAH, levels in wet depositions are higher in winter than in summer. The behavior of PAHs has been explained both by the increase of pollution sources in winter due to domestic heating and by a longer retention time of these compounds in the atmosphere at lower tem­peratures. Since aerial pollution decreases logarith­mically with the increase in distance from the source, it is obvious that its impact on lakes is greater in the vicinity of anthropic activities, as can be inferred by the concentrations of micropollu­tants in air and rain.

In the Great Lakes region, the atmospheric input of PCBs derives mainly from wet depositions with concentrations ranging between 50 and 215 ng/1, higher by far than those of remote regions (see Ta­ble II). No significant differences in PAH concen­tration can be found in rain and water from differ­ent geographical areas, since these compounds are mainly associated with particles and reach the aquatic environment through dry deposition.

B. Land Runoff Runoff from land may also contribute substantial quantities of PAHs to the aquatic environment. Runoff waters from a British motorway contained

Table II Organic Micropollutants in Rain and Snow (ng/1)

a-HCH γ-HCH pp'DDE Atr Sim Tba PCBs BaP F B(ghi)P

Canada, 1986 articsnow 0.43-8.70 0.22-5.31 nd-0.07 — — — 0.02-1.76 —

United States, 1985 winter rain — — — nd nd — — — summer rain — — — nd-1500 nd-500 — — —

Switzerland winter rain — — — nd" nd-1.1" nd-9.6" — 25* 400* 25'· summer rain — — — 2.4-600" 1.2-121" 0.4-198" — 4* 20* 4* snow — — — nd" nd" nd" — 35* 160* 20*

Italy, 1984-1986 winter rain — 4.4-6.9 — — — — — — 20-36 — summer rain — 17-28 — — — — — — 227-204 —

The Netherlands, 1983 rain — _ _ _ _ _ _ 15-37 138-204 39-68

Abbreviations: cx-HCH, a-hexachlorocyclohexane; γ-HCH, lindane; Bap, benzo(fl) pyrene; F, fluoranthene; B(g,/*,/)P, benzo(gA/ perylene; Atr, atrazine; Sim, simazine; Tba, terbutylazine; nd, not detectable.

" 1987. * 1988-89.

494 Organic Micropollutants in Lake Sediments

up to 3.1 μg/l of total PAHs including 0.57 /ig/1 of benzo(a)pyrene (BaP). PAH land runoff to the aquatic environment is estimated at 1.2% of the to­tal, while BaP land runoff is 17% of the total from all BaP sources.

As far as PCBs are concerned, it is well recog­nized that a large amount of wastes have been de­posited in lagoons, landfills, and open dumps. Even if statistics are not highly accurate, an estimate of the distribution and fate of PCBs in the United States shows that 27% of the total production since 1929 is in landfills and 16% either is in the environ­ment or has been destroyed. PCB disposal repre­sents a potential source of pollution that can last over a long period of time.

Runoff from cultivated land is the major source of pesticide pollution to inland water bodies: the extent of this phenomenon depends on the amount applied per unit of area (yearly turnover), the com­position of the soil, and the physicochemical properties of the pesticide. Most of the data on ag­ricultural runoff refer to herbicides because they are used in large amounts on soil and include a se­ries of compounds easily leached from soil because of their relatively high water solubility. Mobility, in fact, is proportional to water solubility and in­versely proportional to Kow and Koc, and is exactly the opposite of adsorption capacity. Runoff losses of herbicides are highest if the runoff occurs soon after herbicide application. For atrazine, one of the most used herbicides in corn and maize growing areas, runoff losses of 0.1-2.9% of the amount ap­plied have been calculated based on concentrations measured in rivers draining some corn-growing ba­sins in Quebec.

After the application, pesticide leaching depends on its persistence in soil. Persistent pesticides are also released from treated soils during winter thaws. In northern agricultural regions, there is ex­tensive flooding of fields because the drainage ditches are blocked with ice. After snow melting and runoff, the pesticides released from soils are discharged from the watershed into lakes.

C. Point Sources Thousands of chemicals enter the environment in this technological era due to chemical manufactur­ing activities, product utilization, and energy plants. On a local scale, the spectrum of potential pollutants is much wider than that of ubiquitous contaminants. Less persistent and accumulable

chemicals may reach lake sediments if they are de­livered in amounts considerably larger than the re­ceiving capacity of the drainage basin.

The identification of local contaminants requires a detailed knowledge of human activities within a watershed, which is generally lacking; information on sources and fate are therefore mainly available for widespread pollutants. A large number of in­dustries produce wastewaters containing PAHs. Commonly cited as industrial sources are oil refineries, the plastic and dyestuff industries, high temperature furnaces, and the lime industry. BaP concentrations in the mentioned wastewaters vary from undetectable to 1000 μg/l.

Domestic wastewaters including raw sewage and storm sewer runoff may contain significant quanti­ties of PAHs. PAH concentrations in sewage in­crease substantially following heavy rains presum­ably because of sewer runoff from roadways (see Table III). Hydrocarbons (λζ-alkanes) and chlori­nated hydrocarbons (e.g., HCHs, DDTs, PCBs) have also been determined at significant levels in urban sewages (see Table IV). Wastewater treat­ment is not 100% efficient and residual chemicals, including intermediates from treatment processes, may be discharged into the effluent reaching the receiving surface waters (see Table IV).

Wastewaters from tanneries may contain large amounts of chlorinated pesticides. In a tannery dis­trict in Northern Italy, unusual concentrations of

Table III Concentration of PAH ^g/l) in Domestic Sewage from Hegne (GFR)

Compound Dry weather During

heavy rain

Fluoranthene 0.352 16.35 Pyrene 0.254 16.05 Benzo(a) antrhacene 0.025 10.36 Benzo(Z?) fluoranthene 0.039 10.79 Benzo(/) fluoranthene 0.057 9.91 Benzo(£) fluoranthene 0.022 1.84 Benzo(a) pyrene 0.001 3.84 Benzo(g,h,i) perylene 0.004 4.18 Indeno(l,2,3-c,i/) pyrene 0.017 4.98 Total unidentified PAH 0.075 9.20 Total PAH 0.846 87.50

Source: From Borneff and Kunte (1965). In Neiff, J. M. (1979), "Polycyclic Aromatic Hydrocarbons in the Aquatic Environ­ment." Applied Science Publishers, London. Reproduced with permission.

Organic Micropollutants in Lake Sediments 495

Table IV Chlorinated and Aliphatic Hydrocarbons (/*g/l) Identified in Urban Sewage

Location PCB DDTs γ-HCH n-Alkanes

Toulon-east, France (I) 0.141 ±0.052 0.239±0.327 0.220±0.050 274 (E) 0.089±0.054 0.190±0.168 0.215±0.031 26

Morlaix, France (I) 0.046±0.034 0.013±0.009 0.045±0.026 — (E) 0.25±0.011 0.003±0.001 0.021 ±0.021 —

Nantes-north, France (I) 0.14±0.31 <0.02±0.21 <0.02 130-453 (E) 0.08 <0.02 <0.02 74-94

Nantes-south, France (I) 0.17-0.44 <0.02 <0.02-0.24 80-132 (E) <0.02 <0.02 <0.02-0.05 <0.5-3.4

Marseille, France 0.11 — 0.12 — Oxford, U.K. 0.05-0.08 0.03 — — New York 0.02-0.9 — — — Los Angeles 0.94 0.94 — — Kalamazoo River WWTP, USA 0.4 — — — Various sewages, USA 0.54-3.05 0.02-1.05 0.11-0.05 —

Source: Modified from Marchand, Μ., et αϊ. (1989). Organic pollutants in urban sewage and pollutant inputs to the marine environment. Application to the French shoreline. Wat. Res. 23, 461. Reproduced with permission.

Abbreviations: I, treatment plant influent; E, treatment plant effluent.

HCH isomers and DDTs were found in waters con­taining one-half civil and one-half industrial dis­charges (see Table V). This was due to the leather conservation treatment in African countries from which the leather was imported. According to the adsorption properties of these insecticides, a con­siderable part of this contamination is transferred to the activated sludge (see Table V).

Rivers receive most of the urban, industrial, and agricultural discharges. In many situations, lake tributaries represent point sources of pollution for a number of organic compounds. The total quantity of dissolved pollutants in lakes increases depending upon the morphological characteristic of the lakes themselves (i.e., renewal time, volume). The pol­lutants vehiculated by suspended solids are depos-

Table V Concentration of Chlorinated Pesticides (/u,g/l) in a Treatment Plant Receiving Tannery Effluents 0

Sample a-HCH γ-HCH pp'DDT op'DDT pp'DDE pp'DDD XDDT

Sewer 132 53 20.2 4.6 0.5 1.5 26.8

WWTP tank* 72 0.9 — — 1.0 3.2 4.2

WWTP effluent 38 0.9 — — 0.3 0.5 0.8

WWTP mud'' fresh 59 — — — 142 351 493 2 months — — — — 286 1182 1468 5 months 52 8 — — 3030 9361 12391

Source: Modified from Galassi et al. (1983). Presenza di pesticidi clorurati in acque di scarico di conceria. Acqua & Aria 6, 601. Reproduced with permission.

a Waste water treatment plant, homogenizing tank. b In Mg/kg dry weight.

436 Organic Micropollutants in Lake Sediments

ited in lake sediments according to the pattern of the current. Several examples of 4'hot pollution" areas have been identified in deposition zones of incoming tributaries. This fact partly accounts for the wide range of concentrations measured within a single lake (see Section V).

II/. Analysis

A. Sampling and Sample Handling Two main categories of sediment samplers are usu­ally employed: grabs and corers. Grabs produce large samples of known surface from the top layers of sediment, but the degree of penetration into the sediment is not predictable. Furthermore, grab sampling causes a perturbation of the water/ sediment interface and a sediment mixing. Grab samplers, therefore, do not allow the attribution of the collected sample to the corresponding sedimen­tation period. Corers, on the contrary, give a lower disturbance of the sediment and also allow the col­lection of deep layer sediments. Historic patterns of pollution may therefore be reconstructed, ana­lyzing the sediment layers obtained by cutting the core in slices corresponding to a certain period of time, provided that the sedimentation rate of the lake is known. The sedimentation rate is usually calculated measuring the 1 3 7Cs decay, taking into account the effect of density and porosity of the sediment.

8. Extraction Sediment samples are usually freeze-dried before extraction. However, organic micropollutants can also be recovered from wet sediment, providing that extraction solvents of decreasing polarity are used. Dehydrating chemicals, such as anhydrous sodium sulfate, can also be added to wet sediment instead of drying it or using intermediate solvents.

Numerous solvents have been used, in conjunc­tion with a solid extraction technique, to recover organic micropollutants bound to sediments. Due to their low polarity, hydrocarbons such as pen-tane, hexane, or cyclohexane are employed for ly-pophilic compounds such as Ai-alkanes, PCBs, and DDTs. More polar solvents such as benzene or methylene chloride are usually used for the extrac­tion of PAHs, phthalates, and herbicides.

Continuous solvent extraction is generally per­formed with a Soxhlet apparatus, but good recov­eries are also obtained by sonication. This last technique is much faster than Soxhlet extraction and requires very small amounts of solvent. Since many solvents may contain some impurities that in­terfere with subsequent analytical determinations, in many cases it is very convenient to limit the volume of the extractant. This is the case with phthalates that are ubiquitous contaminants of sol­vents, glassware, and laboratory equipment.

C. Cleanup Many natural compounds of biogenic origin may occur in lake sediments. In productive lakes, much of the organic detritus accumulating in surface sed­iments is derived from biota occurring within the water column. The lipid fraction of these sediments includes «-alkanoic acids, branched/cyclic alkanoic acids, alkenoic acids, and fl-alkanes.

Diagenetic compounds are coextracted with or­ganic micropollutants, with which they may inter­fere during the analytical determinations. For this reason, cleanup procedures are usually required before analysis in order to prevent contaminations of the analytical apparatus and to render analysis easier.

Column chromatography has been extensively used to separate organic micropollutants from other organic compounds, as well as one class from another among the former. Thin-layer chroma­tography (TLC) may also be used as a separation technique.

Alumina, silica, Sephadex, and Florisil column chromatography have been widely applied for the cleaning-up of sediment extracts. However, the cleanup procedure should be chosen as a function of the subsequent analysis.

D. Analytical Procedures Gas-liquid chromatography (GC) is the primary technique for the separation and quantitative deter­mination of organic micropollutants. Due to partic­ularly difficult separation problems, high-resolution gas chromatography is required for the analysis of environmental samples. Flame ionization detection is usually coupled to GC for Ai-alkane, PAH, and phthalate determinations. Electron capture detec-

Organic Micropollutants in Lake Sediments 437

tion is used for PCBs and DDTs and selective ni­trogen/phosphorus detection for herbicides.

High-performance liquid chromatography (HPLC) has also been applied to the analysis of PAHs. Fluorescence spectrometry coupled with HPLC allows a very sensitive analysis of PAHs without the need for complicated cleaning-up pro­cedures, due to the high selectivity of the detector.

One drawback of GC and HPLC analysis is the lack of positive identification of the compound which gives rise to a certain peak. GC-mass spec­trometry (GC-MS) allows unequivocal quantitative analysis. However, since the use of the mass spec­trometer as a detector often gives lower sensitivi­ties than selective detectors, the use of GC-MS can not always be applied. GC analyses making use of capillary columns of different polarities, HPLC, and TLC may be used as confirmatory techniques.

ΙΛ Environmental Data

A number of data are available for those com­pounds that have a worldwide distribution (such as PAHs and chlorinated hydrocarbons), but only scattered informations are reported for the other organic micropollutants. An overview of concen­tration levels from different lacustrine environ­ments and within a single lake may give an insight of the pollution status, provided that the data are obtained by similar analytical procedures. For this reason, the most recent data have been selected, and only in a few cases have the older ones been reported for comparison.

A. PAHs As PAHs derive from various sources, the result­ing PAH compounds in sediments are complex and contain a great number of individual PAHs that can not be resolved even by the modern analyti­cal techniques. Characterization is limited to the detection of some individual species, primarily benzo(a)pyrene (BaP), anthracene (A), and fluo-ranthene (F) (see Table VI), although in a few cases up to 64 compounds have been identified. A selection of these data is presented in Table VII.

Fluoranthene is one of the main anthropogenic PAH compounds and is an excellent representative of this class since it is abundant in sediment, is as­sociated with a combustion origin, and is corre­

lated with the majority of the other PAHs with the exception of perylene, dibenzo(a,c/a,h) and inde-no(c,i/)pyrene. It is generally agreed that fluoran­thene concentrations in sediment lower than about 400 μ^/kg are typical of rural or remote areas while higher values are found in industrial or urban areas. If there are no local sources and street runoff is negligible, PAH concentration is in good agreement with the atmospheric load.

Since PAHs are also formed by biogenesis, a background level is to be expected even in unpoll­uted sediments. Preindustrial values of F are gener­ally in the order of 10 μg/kg or less. Since then, concentrations have increased with different pat­terns in the various geographical areas, according to usage of fossil fuels. Examples are presented in Figure 1.

The concentration of BaP has been measured in a large number of freshwater sediments, primarily from European lakes (see Table VI). Sediment BaP concentrations may vary by a factor of 1000 within a single lake, possibly because of different sedi­mentation rates or degrees of biogenesis in differ­ent regions of the lake. When sedimentation rates are high, a seasonal cycle may be detected, not so much because of a changing equilibrium between biosynthesis by sediment anaerobes and degrada­tion by sediment aerobes, but mainly because of the possible seasonal variation in the rate of BaP input.

A high value of BaP in Lake Cayuga sediments was measured in a sampling station located below a highway bridge. This behavior is frequently ob­served in other lentic environments.

β. Chlorinated Hydrocarbons Chlorinated pesticides and PCBs have been recog­nized as a very relevant ecological problem since the sixties and for this reason they have been banned or limited in most European and North American countries. In spite of these restrictions, surficial lake sediments from these areas remain polluted by these contaminants (see Table VIII). Among the reported data, only in the most recent sediments (1986) from Lake Superior PCB concen­trations are significantly lower than those deter­mined several years earlier.

The positive consequences of the adopted regu­lation of PCB and DDT usage are well exemplified by the historical trend of their concentration in

498 Organic Micropollutants in Lake Sediments

Table VI Benzo(a)pyrene (BaP), Anthracene (A), and Fluoranthene (F) in Lake Sediments fag/kg)

Location BaP A F

Rubleskoye Reservoir, USSR 44 — —

Khiminskoe Reservoir, USSR 390-500 — — Grosser Ploner See, FRG 1610 — 560-300 Lake Constance, FRG 443 — 400-1000 Greifensee, Switzerland — — 420 Lake Varese, Italy 69 18 82-192 Lake Comabbio, Italy 37-118 5-17 89-253 Lake Monate, Italy 25-41 3-8 62-128 Lake Superior, USA — nd-10 36-153 Lake Sagamore, USA 128 21 80-463 Woods Lake, USA 690 32 320-1250 Lake Cayuga, USA nd-2000 nd-620 19-3900 Mirror Lake, USA nd nd 600-1000 Northern Lake George, USA — — 160 Marion County Lake, USA — — 140 Lake Luise, USA — — 375 Lake Haiyaha, USA — — 96 Lake Husted, USA — — 110 Lake Loch, USA — — 80 Lake Meade, USA — — 10 Mono Lake, USA — — 13-74 Utah Lake, USA — — 70

Abbreviation: nd, not detectable.

Lake Ontario sediments (see Fig. 2). A continuous increase was observed with the maximum peak oc­curring in the late 1950s for DDTs and in the mid-1960s for PCBs. In both cases, there is a good agreement between the core record and the pro­duction or history of use. The occurrence of DDT in the surficial sediment of African lakes (see Table VIII) is probably due to its present use in de­veloping countries.

C. Phthalate Esters Phthalate esters were introduced into the high polymer materials market in the 1920s and bis(2-ethylexyl)phthalate (DEHP), the most highly pro­duced phthalate ester, was first synthesized in 1933. Since the 1940s, their production rates have shown a rapid increase. The levels in sediment chronologically follow the increasing commercial use of these compounds (see Fig. 3).

As previously pointed out, serious contamination problems may be associated with the analysis of these substances, as phthalate esters are ubiquitous contaminants and are present in some common lab­oratory items. For this reason only a few data on sediment are available (see Table IX).

D. Phosphate Esters Phosphate esters have been widely used since the 1940s as fire retardant plasticizers in synthetic polymers, hydraulic fluids resistant to high temper­atures, and lubricant additives. This class of com­pounds is very large, including akyl, aryl, aryl/ alkyl, and haloalkyl phosphates. The most fre­quently detected in sediments are the less water soluble aryl/alkyl phosphates (see Table X). However, even the more soluble phosphates are detected in lake sediments when direct discharges are present. A typical example is given by tris-

Organic Micropollutants in Lake Sediments 499

Table VII Individual PAHs (/xg/kg) Found in Lake Sediments

Lake Superior

Lake Sagamore

Woods Lake

Lake Cayuga

Phenanthrene 62-98 154 324 49-660

Pyrene 21-88 320 934 <22-3500

Benzo(tf)fluorene — 91 294 — Benzo(a)anthracene 29-65 78 362 <9-1700

Chrysene/triphenylene 73-172 191 888 14-2000

Benzo(b)fluoranthene 104-319 358 1784 nd-3500*

Benzo(/c)fluoranthene 49-197 115 558 — Benzo(^)pyrene 51-103 165 768 nd-1500

Perylene — 605 280 nd-540

Indeno(c,i/)pyrene 91-404 315 1294 7-1500

Dibenzo(tf, cla, /i)anthracene 15-125 30 92 nd-870

Benzo(g, h, i, )perylene 41-216 303 1356 nd-1600

Coronene — 188 801 — Dibenzo(fl,e)pyrene — 15 394 — Retene — 191 270 — 7,12c*-dimethyl-l,2,3,4,4a

11,12,12a-octahydrochry sene 90 100 —

3,4,7-trimethyl-l,2,3, 4-tetrahydrochrysene 20 200 —

Benzo(g, h, Ofluoranthene — — — nd-380

Dibenzothiophene — — — nd-260

Fluorene 4-8 — — —

Source: Modified from Heit, M. (1985). The relationship of a coal-fired power plant to the levels of polycyclic aromatic hydrocarbons (PAH) in the sediment of Cayuga Lake. Water Air Soil Pollution 24, 41. Reproduced with permission.

Abbreviation: nd, not detectable. a Sum of benzo(b) and benzol) fluoranthene.

monochloroisopropyl phosphate (TCIPP) in Lake Varese and Comabbio (see Table X), where con­centrations in water up to 18 /xg/1 were also mea­sured. The rapid increase of the synthetic polymer industry corresponds to the levels in sediment dur­ing the last years (see Fig. 4).

£. Aliphatic Hydrocarbons Petroleum hydrocarbons from oil spills are able to persist in sediments for a long time. The odd-carbon predominance reflects the composition of organic matter of biogenic origin. ft-Heptadecane (Cn) in particular is very abundant in surficial sedi­ments of productive lakes because it is produced by algae decomposition. The isoprenoid hydrocar­bon pristane (C2o), on the contrary, is one of the major constituents of many crude oils.

The concentration of total aliphatic hydrocar­bons in surficial sediments of polluted lakes is higher than that in polluted sediments at least by a factor of ten (see Table XI). Az-Alkanes represent a small fraction of total hydrocarbons. The n-C^I pristane ratio gives an idea of the occurrence of natural hydrocarbons in comparison with those that are anthropogenic.

I/I. Bioavailability and Environmental Hazards

A. Sorption/Desorption The partitioning of a chemical between sediment and water can be described by

500 Organic Micropollutants in Lake Sediments

2-5 J

1910 1920 1930 1940 1950 1960 1970

Figure 1 BaP concentrations in the annual layers of sediments from the northern (built-up area, upper line) and southern (forest, lower line) regions of the Grosser Ploner See (GFR). [From Grimmer, G., and Bohnke, H. (1975). Profile analysis of polycyclic aromatic hydrocar­bons and metal content in sediment layers of a lake. Cancer Lett. 1, 75. Reproduced with permission.]

Table VIII Concentrations of Chlorinated Hydrocarbons (/Ag/kg) in Lake Sediments0

Lake Year PCB XDDT pp'DDT pp'DDE a-HCH γ-HCH HCB

Siskiwit Lake, Canada 1983 48 — — — — — —

Lake Superior, USA 1973 <2.5-57 — — <0.25-23 — — — [9] (0.5)

1977 5-390 — — — — — — (170)

1986 5.3-11.7 — — — — — — [8.6]

Lake Ontario, USA 1968 <5-280 0.4-218 — 0.4-70 — — — (57) (42.8) (12.7)

1981 (570) (141) (18) (51) (1.5) (1) (100) Lake Michigan, USA 1977-80 1-2370 — — — — — — Lake Huron, USA — 9-33 — — — — — — Lake Erie, USA — 74-252 — — — — — —

Lake Geneva, Switzerland 1979 20-540 0.5-49 — — — — — (43) (9.8) (1.5) (3.7) (1) (1) (1)

Lake Garda, Italy 1989 (89) (14) (0.9) (9) (0.3) (0.6) (0.4) Lake Varese, Italy 1988 165 — — 3.7 — — — Lake Comabbio, Italy 1988 87 — — 11.8 — — — Lake Monate, Italy 1988 43 — — 0.6 — — — Lake Mcllwaine, Zimbabwe 1988 — — 32-146 — — — —

(76)

Abbreviation: HCB, hexachlorobenzene. a Values in brackets represent means.

Organic Micropollutants in Lake Sediments 501

Sediment depth (cm)

Figure 2 Chlorinated hydrocarbon concentrations versus sedi­ment depth and age. [Modified from Oliver, B. G. et al. (1989). Distribution, redistribution, and geochronology of polychlori-nated biphenyl congeners and other hydrocarbons in Lake On­tario sediments. Environ. Sei. Technol. 23, 200. Reproduced with permission.]

where Kp is the sediment/water partition coeffi­cient, C s is the amount of chemical sorbed per unit mass of sediment, and C w is the amount of chemical in aqueous phase per unit mass of so­lution.

Equilibrium Kp values for a given hydrophobic solute sorbed on a series of sediments are propor­tional to the fraction of organic carbon (f o c) of the sediment, being

^ o c Kp/foo

where Koc is the partition coefficient on sediment as defined in Section II.

The availability of sorbed chemicals to aquatic organisms depends on the rate of desorption rela­tive to the exposure time. The rate of desorption appears to depend on the magnitude of Kp for hy­drophobic solutes. As a first approximation, the characteristic time (in minutes) for slow desorption seems similar to the numerical value of Koc. In a lake, the possibility of reaching the equilibrium condition between water, suspended solids, and sediments depends not only on the lipophilic nature

180-1

140 4

"I ioo Η

60

20

100 J

60

20

60

20

DEHP

DBP

π r DEP

Figure 3 Variation of phthalate ester concentration as a func­tion of sediment depth and time. The dotted lines represent background levels. [From Peterson, J. C , and Freeman, D. H. (1982). Phthalate ester concentration variations in dated sedi­ment cores from the Chesapeake Bay. Envir. Sei. Technol. 16, 464. Reproduced with permission.]

Deoth 100 90 80 70 60 50 40 30 20 10 0

1923

1929

1935

1940

1946

1952

1957

1963

1968

1974

1979

(cm) Date

502 Organic Micropollutants in Lake Sediments

Table IX Concentrations of Phthalate Esters ^g/kg) in Lake Sediments

Lakes DEHP DBP DEP DPP DAP DIBP BBP

Chesapeake Bay, USA 12-180 27-89 22-42 5.9-13 <1 5.6 —

American lakes (several) — — — — — — 428 Lake Constance, Switzerland 500 200 — — — — —

Lake Superior, USA 200 100 — — — — —

Abbreviations: DEHP, bis(2-ethylhexyl)phthalate; DBP, dibutylphthalate; DEP, diethylphthalate; DPP, dipropylphthalate; DAP, di(2-propenyl)phthalate; DIBP, bis(2-methylpropyl) phthalate, BBP, butylphenylmethyl phthalate.

of the chemical but also on certain characteristics of the water body (residence time, water stratifica­tion, sedimentation rate, etc.) and on the type of the immission of the contaminant (continuous, dis­continuous, or occasional) into the lake.

As a general guideline, under equilibrium condi­tions, all the water from the top of the water col­umn to the bottom of the biotic zone in a settled sediment can be considered as sediment interstitial water. In this case, the exposure concentrations or bioaccumulability can be calculated on the basis of partitioning.

Some exceptions to this general behavior may be observed for polar and ionizable organic com­pounds. In these cases, the equilibrium condition between water and sediment is not governed by the organic carbon content because of specific interac­tion with sediment surface functional groupings. The same seems to be true for PAH, since some reported data show that water PAH concentrations are between two and five orders of magnitude lower than those calculated from sediment concen­trations, assuming equilibrium partitioning.

Table X Concentrations of Phosphate Esters (μ-g/kg) in Lake Sediments

Lakes TPP NPDPP CPDPP TCIPP

Lake Michigan, USA Waukegan Harbor 0.01 0.2-0.6 0.05-0.2 — Waukegan Bay nd nd nd —

Lake Varese, Italy — — — 0.30 Lake Comabbio, Italy — — — 0.86 Lake Monate, Italy — — — nd

Abbreviations: TPP, triphenylphosphate; NPDPP, nonyl-phenyldiphenylphosphate; CPDPP, cumylphenyldiphenylphos-phate; TCIPP, trismonochloroisopropylphosphate; nd, not de­tectable.

B. Biological Effects The main route for bioaccumulation at the lower trophic levels of the food web is the direct assump­tion of the chemicals from water. However, in freshwater environments, some organisms, such as oligochaetes and chironomids, are sediment in-gesters. Benthic invertebrates could therefore rep­resent an important dietary source of contaminants for predators. Furthermore, these organisms are also responsible for bioturbation of settled sedi­ments causing sediment mixing. Contaminated sed­iments of the biotic zone could be resuspended and become available for exchanges with the overlying surface water. Deep sediments can be more con­taminated than surficial ones because of previous emmissions of pollutants into the water body or to sedimentation of contaminated material at higher rates than those needed to establish equilibrium ex­changes between suspended matter and water.

Besides the risk for bioaccumulation, the con-

0-1 1 1 1 1 1 1

67 71 75 79 83 87 91 years

Figure 4 Temporal trend of trismonochloroisopropyl phos­phate concentration in Lake Comabbio sediments.

Organic Micropollutants in Lake Sediments 503

Table XI Concentrations of Aliphatic Hydrocarbons (/xg/kg) in Lake Sediments

Lakes Total n-alkanes Az-Ci 7H 3 6/pristane

Lake Constance, Switzerland 320 — —

Lake Zug, Switzerland 50-900 — 1-2.8 Lake Washington, USA 1400 10 — Various unpolluted lakes, U.K. 37 — —

taminants in sediments might represent a potential source of toxicity to the organisms. An understand­ing of sources and effects of complex mixtures re­quires the complete chemical characterization of sediments. However, residue analyses are time-consuming and expensive, and they enable one to determine toxicant concentrations only as a func­tion of the efficiency of the extraction and not of their availability to biota. Therefore, bulk chemical analysis of sediment cannot be used directly to pre­dict biological responses. In addition, the concen­trations of single chemicals are usually compared with known dose-response relationships, while the global effects of toxicants in the real environment

are also the result of the interactions among toxi­cants.

Because of these problems, biological assays have been proposed to screen the sediment quality and the potential risk to benthic organisms. Two procedures are usually employed to perform eco­toxicological tests on sediments. The first uses aqueous extracts (elutriate), giving an idea of the potential toxicity of resuspended sediments in the water column. The second uses the whole sediment, diluting it with reference noncontaminated sediment, in order to obtain a dose-response relationship.

An example of toxicity of harbor sediment in the Lake Ontario is shown in Figure 5. In this case the

Burlington

Ontario

Hamilton

Figure 5 Toxicity of Hamilton Harbor sediments to Photobacterium. [From Brouwer, H., et al. (1990). A sediment-contact bioassay with Photobacterium phosphoreum. Environ. Toxicol. Chem. 9, 1353. Reproduced with per­mission.]

504 Organic Micropollutants in Lake Sediments

toxicity was determined on Photobacterium using whole sediment. The relative importance of the in­terstitial water and the whole sediment depends on organism and toxicant type. It is therefore gener­ally agreed that both elutriate and sediment should be tested with a battery of tests, including a series of species representative of different trophic levels.

In conclusion, even if there is a general consen­sus for developing and promulgating sediment wa­ter criteria, it is recognized that at this time it is not feasible to establish numerical sediment quality cri­teria, because of the lack of a unified approach to assess the potential hazard of sediment-bound chemicals.

Related Articles: AQUATIC TOXICOLOGY, ANAL­YSIS OF COMBINATION EFFECTS; CHROMIUM; SOIL DECONTAMINATION .

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tracers of particulate dynamics in large lakes. J. Great Lakes Res. 15, 84-103.

Baudo, R., Giesy, J. P., and Muntau, H., eds. (1990). "Sedi­ments: Chemistry and Toxicity of In-Place Pollutants." Lewis Publishers, Ann Arbor, MI.

Dickson, K. L., Maki, A. W., and Brungs, W. Α., eds. (1987). "Fate and Effects of Sediment-Bound Chemicals in Aquatic Systems." Pergamon Press, New York.

Donze, M., Nieuwendijk, C , and Van Boxtel, A. (1990). "Aquatic Pollution and Dredging in the European Commu­nity." Delwel Publishers, The Hague.

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Kenaga, Ε. Ε., and Goring, C. A. I. (1980). Relationship be­tween water solubility, soil sorption, octanol-water parti­tioning, and concentration of chemicals in biota. In "Aquatic Toxicology," (J. G. Eaton, P. R. Parrish, and A. C. Hen­dricks, eds.). American Society for Testing and Materials, STP 707,78-115.

Oliver, B. G., Charlton, Μ. N., and Durham, R. W. (1989). Distribution, redistribution, and geochronology of poly-chlorinated biphenyl congeners and other chlorinated hydro­carbons in Lake Ontario sediments. Environ. Sei. Technol. 23, 200-208.

Rand, G. M., and Petrocelli, S. R., eds. (1985). "Fundamentals of Aquatic Toxicology." Hemisphere Publishing Corpora­tion, Washington, D.C.

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