Health, Zagreb, Republic of Croatia. Reviews compound physico- chemical properties and water and soil properties influencing the transport and distribution of ...
Persistent organochlorine compounds in water and soil environments
˘elimira Vasilic´ Laboratory for Vlasta Drevenkar, Sanja Fingler, Zlatko Fröbe, Z Organic Analytical Chemistry, Institute for Medical Research and Occupational Health, Zagreb, Republic of Croatia Reviews compound physicochemical properties and water and soil properties influencing the transport and distribution of organochlorine pesticides, polychlorinated biphenyls (PCBs) and chlorophenols in a water and soil environment. As highly hydrophobic compounds of low water solubility, organochlorine pesticides and PCBs are rapidly and strongly sorbed by most soils and sediments. The sorption of weakly acidic chlorophenols comprises both molecular and ionic forms and depends not only on the soil/sediment organic matter content but also on the pH and ionic strength of the aqueous phase. Briefly describes the analytical methods for trace analysis of organochlorine pesticides, PCBs and chlorophenols in water and soil/sediment samples. Presents some results of those micropollutants’ analysis in surface, ground and drinking waters, soils, river sediments and wet depositions in Croatia.
Environmental Management and Health 7/4 [1996] 5–8 © MCB University Press [ISSN 0956-6163]
Persistent and toxic organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs) and chlorophenols (CPs) belong to the micropollutants of water and soil environments distributed worldwide. The use of OC pesticides has been restricted or banned in most developed countries but continues in developing countries. PCBs are a group of 209 congeners which have been widely used as heat transfer fluids, hydraulic fluids, flame retardants and dielectric fluids. For their easier handling a systematic numbering has been introduced and widely accepted as PCB numbers[1]. In developing countries PCBs have been substituted only partially. CPs, particularly those with three and more chlorine atoms have been used as fungicides with main applications in the preservation of wood, leather and textiles as well in pulp and paper industries. They are also intermediates in the production of phenoxy herbicides and degradation products of hexachlorocyclohexane and chlorobenzenes. CPs can also be formed by routine disinfection of drinking water by chlorination as a result of chlorination of phenols and as by-products of the reaction of hypochlorite with phenolic acids. OC pesticides, PCBs and CPs enter the environment either directly, mostly through the pesticides application and uncontrolled waste discharge, or indirectly through atmospheric transport. Their levels and distribution in the environment need to be controlled by means of an environmental risk assessment. PCBs are considered to be the main precursors of highly toxic polychlorinated dibenzo-pdioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). PCDD and PCDF traces are contained also in technical tri-, tetra- and pentachlorophenol formulations. In this paper some factors influencing the behaviour of persistent and lipophilic OC compounds in water and soil environments and the analytical methods for analysis of OC pesticides, PCBs and CPs in aqueous and soil/sediment samples are briefly described. The environmental levels of those pollutants are illustrated by selected results of OC pesticides, PCBs and CPs analysis in different waters, soils, river sediments and wet depositions in Croatia.
Factors affecting transport and distribution of PCBs, OC pesticides and CPs in water and soil environments The behaviour of OC compounds in water and soil environments depends on both the specific compound properties and on the water and soil properties. Major physico-chemical properties from the environmental point of view are compound water solubility, lipophilicity and volatility (Table I). Compound lipophilicity is characterized by octanol/water partition coefficient Kow, which correlates well with its water solubility, soil sorption and bioaccumulation. As highly hydrophobic compounds of low water solubility OC pesticides and PCBs are rapidly and strongly sorbed by most soils[2,3] and in aquatic systems they are often associated with bottom sediments[4,5]. Due to their low degradability these compounds accumulate in sediments and aquatic organisms relative to the concentration found in water. The sorption of PCBs is favoured by high soil total organic carbon, high total aluminium and iron oxides and high content of fine particles like silt[2]. Sorption of CPs to bottom sediments is expected to be lesser than that of OC pesticides and PCBs because of their lower Kow values (Table I). CPs are weak organic acids with acidities in the pKa range from 5 to 9. At typical ambient pH values, CPs, in particular the highly chlorinated and more acidic tetraand penta-CPs, are present in the aqueous environment predominantly as phenolate anions. The sorption of CPs comprises both molecular and ionic forms[6,7] and depends on the pKa and Kow of the particular CP, on the pH and ionic strength of the aqueous phase[7,8] and on the soil organic carbon content[7,9]. In some cases a strong interaction of chlorophenolates with organic-free mineral surface was observed[9]. Some charged species in the sorbent material, such as Ca2+ and Mg2+ ions also influence the CPs sorption[6]. Due to strong sorption in most soils the transport of OC pesticides and PCBs through the soil to the surface and ground waters by leaching is very slow or negligible. However,
[5]
Vlasta Drevenkar, Sanja Fingler, Zlatko Fröbe, ˘Zelimira Vasilic´ Persistent organochlorine compounds in water and soil environments Environmental Management and Health 7/4 [1996] 5–8
as the water solubility of CPs increases and their sorption intensity decreases with increase in pH value[7,8], they tend to be transported by leaching especially in neutral, basic and mineral soils with a low organic matter content. The occurrence of OC pesticides, PCBs and CPs in regions where they were not used could be explained only by their efficient atmospheric transport and subsequent wet and dry deposition. Their presence in the rain and snow water[10-12] stems from dissolution of gas-phase organics through gas-rain partitioning and from scavenging of particles and their associated compounds. Chlorophenols have much higher vapour pressures than OC pesticides and PCBs (Table I) and exist in the air almost entirely in the gaseous phase[10]. For these compounds gas scavenging is much more important than particle scavenging. For semi-volatile lipophilic compounds of low water solubility such as PCBs, particle scavenging was shown to be their dominant source in rain water samples[11].
Analysis of PCBs, OC pesticides and CPs in water and soil/sediment Concern about the sources, fate and environmental impact of OC compounds in the aquatic environment has stimulated the development of a variety of sensitive and complex analytical methods for their determination at trace levels both in water and in soil/sediment samples. These methods generally include a preconcentration step which is
Table I Solubility in water (S), octanol/water partition coefficient (Kow) and vapour pressure (vp) of selected OC pesticides, PCBs and CPs Compound isomersa
HCH (α-, β-, γ-) 4,4′-DDTa 4,4′-DDDa 4,4′-DDEa PCBsa Di-, tri-CPb PCPc
S, mol dm–3
log Kow
vp, Pa (°C)
2×10–5 – 7×10–7
3.9
5×10–5 – 2×10–2
(20)
6×10–9 2×10–8 3×10–8 8×10–10 – 1×10–6 4×10–3 – 3×10–2 5×10–5 (20°C, pH 5)
6.0 6.0 5.7 5.5–7.2 3.2–4.4 5.2
3×10–5 1×10–4 9×10–4 8×10–5 – 3×10–2 2.3–11.9 2×10–3
(25) (30) (30) (25) (25) (20)
Notes: S, Kow and vp data taken from [13]; PCB data refer to PCB congeners: 28 (2,4,4′-trichlorobiphenyl), 52 (2,2′,5,5′-tetrachlorobiphenyl), 101 (2,2′,4,5,5′-pentachlorobiphenyl), 138 (2,2′,3,4,4′,5-hexachlorobiphenyl), 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl) and 180 (2,2′,3,4,4′,5,5′-heptachlorobiphenyl)
a
b
S and vp taken from [10], and Kow from [7] and vp taken from [14], and Kow from [7]
cS
[6]
accomplished either by direct solvent extraction[5,15-17] or by adsorption and subsequent elution from an appropriate adsorbent[17-20]. High-resolution capillary gas chromatography (HRGC) with electron capture and mass spectrometric detection enables reliable identification and trace levels quantification of target compounds. Before gas chromatographic analysis, chlorophenols are usually converted into less polar derivatives although gas chromatographic[20] and high performance liquid chromatographic[7] procedures for analysis of non-derivatized chlorophenols are also described. In qualitative and quantitative analyses of PCBs specific problems are encountered due to the complex composition of PCB mixtures both in environmental samples and in commercial formulations, which are often used as standards[21]. PCBs are often quantitated as “total” PCBs: either as the sum of PCB congeners expressed as a mixture or a combination of technical PCB mixtures, or as a sum of PCB congeners expressed as the sum of single congeners present in the sample. HRGC techniques enable efficient separation and quantitation of individual PCB congeners, e.g. congeners selected as typical and representative of the most widely used PCBs: PCB 28, 52, 101, 138, 153 and 180. For an environmental risk assessment the determination of the most toxic co-planar congeners and their moderately toxic mono-ortho analogues is of paramount importance. To minimize the interferences, the determination of nonplanar and co-planar PCB congeners should be preceded by a pre-separation step[22]. For an accurate determination of both ortho- and non-ortho-substituted PCBs a high performance liquid chromatographic pre-separation step was proposed[16]. The choice of analytical methods for studies of OC compounds in water and soil/sediment samples in our laboratory is determined by the equipment at disposal for continuous use and by the necessity to achieve a high detection sensitivity enabling trace analysis. Due to the higher sensitivity of an electron capture detection than of detection by mass spectrometry unambiguous identification of organochlorine compounds in diluted samples has been substituted by concurrent sample analysis on two basically different gas chromatographic columns. Gas chromatographic-mass spectrometric analysis with an ion trap detector is used for more concentrated or pooled samples only. OC pesticides and PCBs are accumulated from aqueous samples by multiple extraction with n-hexane[15] and from soil/sediment samples by sonication of sample with 1:1 acetone:n-hexane mixture[16]. The water extracts are purified by washing with concentrated sulphuric acid and the soil/sediment extracts are treated with copper powder, mercury and finally with sulphuric acid. The
Vlasta Drevenkar, Sanja Fingler, Zlatko Fröbe, ˘Zelimira Vasilic´ Persistent organochlorine compounds in water and soil environments Environmental Management and Health 7/4 [1996] 5–8
accumulated pesticides and PCBs are analysed, without previous separation, on a packed and a capillary gas chromatographic column. PCBs are quantitated against a standard mixture consisting of Aroclor 1242 and Aroclor 1260 in a 2.5:1 ratio either by the individual peak or individual congener method[12]. CPs are accumulated from water samples by C18 reversed phase adsorption followed by elution with acetone and conversion to acetyl and pentafluorobenzoil derivatives[17]. The analysis of both types of derivatives on two different gas chromatographic columns is recommended for a more reliable identification and quantitation of the compounds analysed.
OC pesticides, PCBs and CPs in water and soil/sediment samples in Croatia The use of OC pesticides in Croatia has been restricted for some 30 years. The use of DDT was restricted in 1972 and hexachlorobenzene (HCB) has been prohibited since 1978. γ-Hexachlorocyclohexane (γ-HCH, Lindane) is still produced and used in Croatia. Despite restriction some electricity facilities still contain PCBs. Data on the presence of OC compounds in the water environment in Croatia mostly refer to the analysis of widely distributed OC pesticides. Recent measurements indicate that their levels are generally within ecotoxicologically acceptable limits characteristic of global environmental pollution. To provide an insight into the background levels and risks imposed by the environmental presence of OC pesticides, PCBs and CPs, we investigated the origins and levels of those compounds in surface, ground and drinking
Table II Maximum concentrations of selected OC compounds in waters and wet depositions in the Zagreb city area in period 1992-1995 for γ-HCH and PCBs and 1984-1995 for CPs Maximum concentrations, ng dm–3 Water γ-HCH PCBs 2,4,6-TCP 2,3,4,6-TeCP Sava river 5 25 62 69 Small streams 6 13 17 93 Lakes 2 14 27 2 Ground water 4 1 24 46 Drinking water 1 2 9 10 Rain – water 38 205 69 63 512 4,155 ndb ndb – particlesa Snow – water 6 50 210 527 242 4,082 ndb ndb – particlesa Notes: a Concentration expressed in ng g–1 b Not determined
PCP 163 238 5 151 123
waters, wet depositions, soil and river sediments from different areas in Croatia[12,15,23]. As an example the maximum concentrations of γ-HCH, total PCBs, and most frequently detected CPs: 2,4,6trichlorophenol (2,4,6-TCP), 2,3,4,6tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP), measured over a longer period in different waters and wet depositions in the Zagreb city area, are listed in Table II. As a consequence of the regular use of insecticide formulations containing lindane, γ-HCH was the only pesticide detected in all aqueous samples and in the highest concentrations. All surface, rain and snow waters contained traces of PCBs and most of the particle samples isolated from rain and snow waters contained traces of the DDT-type compounds. PCP was the most abundant chlorophenol in surface, ground and drinking waters. Different CPs appeared regularly in rain and snow water samples and their concentrations in snow water were significantly higher than those in rain water[12]. Data on levels and distribution of OC pesticides, PCBs and CPs in aquifer sediments and soils in Croatia are generally lacking, although they are of crucial importance for evaluation of environmental pollution by those hydrophobic pollutants. The maximum concentrations of PCBs and selected OC pesticides measured recently in surface soils and river sediments from different areas both in continental and in coastal parts of Croatia are shown in Table III. In most of the surface soils and river sediments the background concentrations of total PCBs were lower than 10 µg kg-1. The highest PCB concentrations, listed in Table III, were measured in a surface soil in the vicinity of a transformer station and in a river sediment in the Karst region, pointing to a local source of pollution. The OC pesticides most frequently detected in soil/sediment samples were DDT and its degradation products and γ-HCH. Owing to the high environmental persistence and the highest lipophilicity in the series of pesticides analysed, DDT and its degradation products
Table III Maximum concentrations of PCBs and selected OC pesticides in surface soils and river sediments in Croatia in the period 1993-94 Compound
19 ndb 131 ndb
PCBs HCB α-HCH β-HCH γ-HCH 4,4′-DDE 4,4′-DDD 4,4′-DDT
Maximum concentration, µg kg–1 Surface soil River sediment 165.5 0.3 0.4 0.6 8.3 96.9 10.4 43.9
507.1 < 0.1 < 0.1 0.6 3.5 9.1 2.4 10.4 [7]
Vlasta Drevenkar, Sanja Fingler, Zlatko Fröbe, ˘Zelimira Vasilic´ Persistent organochlorine compounds in water and soil environments
have a high capability of sorption and accumulation in soils and sediments. Consequently, in both soil and river sediment samples the maximum concentrations of DDT-type compounds were higher than those of other OC pesticides.
Environmental Management and Health 7/4 [1996] 5–8
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[8]
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