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Petroleum residues in surface sediments of Kuwait
Volume '6/",:u,~be~ 5/May 19~5
pies of water were collected at depths of 1, 5, 10, 15.20, 30 and 50 m. using Nansen reversing water samplers. The sampling was done during 1981-1982. Measurements of inorganic nutrients were made by methods described by Friligos ( 1982). The total nutrient in the two gulfs was determined for three periods (Tables 1, 2). The approximate volume in the Kavala Gulf is 5137 × 10 ~' m -~ and in the Alexandroupolis Gulf (less deep) 3376 × 106 m 3. The current levels of the circulatory nutrients were estimated by computing mean values station by station and combining these to give mean values. The mean values were multiplied by the appropriate volumes to give quantitive TABLE 2 Nutrient concentrations in the Kavala Gulf Water column averages (gg-at 1-I) PO4-P SiO4-Si NH3-N NO2-N NO~-N
Date
)~N
March 81 August 81 March 82
0.34 0.18 0.13
2.86 1.07 1.54
0.23 0.49 0.36
0.06 0.12 0.06
0.89 0.52 1/.37
1.18 1.13 0.79
Background*
0.12
1.22
0.36
0.16
0.42
0.94
Total nutrients by cruise (g-at × 10 ") March 81 August 81 March 82
1.75 0.93 0.67
14.70 5.50 7.92
1.18 2.52 1.85
0.31 0.62 0.31
4.57 2.67 1.90
6.06 5.81 4.06
Background*
0.62
6.27
1.85
0.82
2.16
4.83
estimates of total nutrients contained in the basins. The mean values for the Aegean calculated in the same way (Friligos, 1981 Table 3) were taken as a basis for comparison. The tendency of the water of the two gulfs to accumulate nutrients above the background level is shown more clearly in Tables 1, 2, where the data have been converted to ratios of total nutrient to background level. Alexandroupolis Gulf contained three times as much silicate and six times as much nitrate than the background, owing to the contribution of the Evros River. Kavala Gulf phosphate levels are twice background, owing mainly to the presence of a fertilizer factory there. However, the nutrient enrichment in the two areas was smaller that that in Elefsis Bay, which is the most industrialized area in Greece, polluted by sewage and industrial effluents and the water of which remain stagnant in summer. Friligos (1981), reported that the Eiefsis Bay contained nine times as much inorganic nitrogen as the same background. This was due mainly to ammonium being 15 times as high as the background value. Nitrate and nitrite were in quantities greater by 7 and 3 times respectively above background, phosphate and silicate were, respectively, about 5 and 4 times above background.
Institute of Oceanographic, and Fisheries Research, Hellenikon, Athens, Greece
N. FRILIGOS
Ratios of total nutrient per cruise to background nutrient March 81 August 81 March 82 Overall means
2.82 1.50 1.80 1.80
2.34 0.88 1.26 1.49
0.64 1.36 1.00 1.00
0.38 0.76 0.38 0.51
2.12 1.24 0.88 1.41
1.25 1.20 0.84 1.10
*Value obtained by multiplying background concentrations by volume of basin under consideration.
Marine PollutionBulletin, Vol.16, No. 5, pp. 2119-211,1985 Printedin GreatBritain
Petroleum Residues in Surface Sediments of Kuwait The local marine environment of Kuwait is exposed to a relatively high chronic input of petroleum hydrocarbons from industrial effluents, sewage and oil spills. Significant anthropogenic input is also due to the heavy oil shipping activities in the small semi-enclosed water body of the Arabian Gulf. Official statistics of Kuwait showed that 69 t crude oil was accidentally spilled in 1979, during which period 106 million t crude oil was loaded. However, this figure may rise to several times as much due to unreported spillage and the input from urban runoff. Experimental evidence suggests that about 56% of spilled oil becomes adsorbed to bottom sediment (Knap & Williams, 1982) where oxidation may take several years (Scarratt & Zitko, 1972; Blumer & Sass, 1972; Thomas, 1973). Thus the degree of oil pollution in the marine environment may be more accurately assessed by measuring oil in sediments rather than in the overlying water column.
Friligos, N. (1981). Enrichment by inorganic nutrients and oxygen utilization rates in Eiefis Bay 11973-1976). Mar. Pollut. Bull., 12, 431-436. Friligos, N. (1982). Some consequences of the decomposition of organic matter in Elefis Bay, an anoxic basin. Mar. Pollut. Bull. 13, 103-106. Therianos, A. D. 11973). The geographical distribution of river water supply in Greece (in Greek). Bull. Geol. Soc. Greece, XI, 25-28.
01125-326X/85 $3.00+0.1)11 ¢) 1985 PergamonPressLtd.
This study provides background information about the distribution of petroleum hydrocarbons in the coastal and offshore sediments of Kuwait prior to the Norwuz oil spill, against which future impacts can be compared. Samples of surface sediment were collected from 66 locations within the territorial waters of Kuwait by Van Veen grab sampler between November 1979 and December 1980. Aliquots of approx. 2 g freeze-dried sediment were extracted in cyclohexane and analysed for hydrocarbons using Turner 430 spectrofluorometer. The procedure was based on that adopted for the IGOSS Project (IOC/WMO, 1976). The fluorescence intensities were measured at 374 nm (excitation at 310 nm) as recommended by Hargrave & Phillips (1975). Measurements were made against API Kuwait crude oil as an arbitrary standard for comparison. Coefficients of variation for replicate analyses of three sediment samples with differrent levels of petroleum hydrocarbons were 13.4, 8.9, and 10.8%. Concentrations of petroleum residues in sediment samples ranged from 1 to 291 gg g-~ dry wt Kuwait crude oil equivalents. However, concentrations exceeding 100 209
IRAQ
BUB]:]:sY,AN
%
t*
.
/" % .
•:.. :~'.....
J,
ppm hydrocarbons = '~
~ 2.0
At Finta! Fi~
~
2.l-IO.O
AL A, Abroad Astt-
~10.1-2.0
Sht'~aibal" ,
Ol~QI I Q
20. I- 35.0 ~
;,lO0.O
PConc. 35-1OO pDrn is not 0
6
12
18 k m
~o
% 2fl •
~o
KUWAIT 24 °
Fig. 1 Distribution of petroleum residues in marine surface sediments.
gg g-t were observed only in five samples from two areas (Fig. 1): (1) the nearshore area opposite to Ahmadi, Shuaiba and Mina Abdulla ports, and (2) the offshore area south of Qaru Island. Concentrations decreased between these two areas, suggesting that oil pollution possibly originated from two different sources: the first from the refineries and ports area, and the second from the offshore drilling and production of oil and/or from natural seeps (Zarba et aL, 1982). Similar conclusions were reached by Douabul et aL (1984) while discussing distribution of petroleum hydrocarbons in surficial sediments from Iraq. The majority of concentrations ranged from 1 to 35 pg g-t, which is comparable to data reported from a nearby region (Douabul et aL, 1984). The lowest hydrocarbon concentration ( < 2 ~tgg- t) were found in the muddy sediments from the turbid shallow waters south of Bubiyan 210
Island and around Failaka island (Fig. 1). Sediment samples from two locations north of Bubiyan Island showed higher levels (12.0 and 13.8 lag g-~) which may be due to oil refinery activities in Iraq and perhaps the maintenance dredging of Khor Abdulla, as suggested by Douabul et al. (1984). The sedimentological charateristics (determined by another research group in our institute) and data on petroleum hydrocarbons were used to cluster the sediment samples in order to investigate possible association between the two sets of data. Ward's Minimum Variance Hierarchical Method was used with data standardization (SAS Library). This analysis divided the samples into seven groups, the characteristics of which are summarized in Table 1: (1) groups II and III showed very high levels of petroleum hydrocarbons, but they differed in all other parameters; (2) groups I and V showed moderate
Volume 16/Number 5/May 1995 TABLE 1
Summary of characteristics of groups formed by cluster analysis Petroleum hydrocarbons (cagg-')
TOC (%)
Average +S.D. CaCO ~
< 63 camfraction
Group No.
No. of observations
I II
6 2
13::I:13 241:1:71
0.7+0.5 0.7+0.1
75+ 8 55=t I
8+4 9±0
III IV V VI VII
2 8 10 25 11
1145:8.5 4.5+4.9 16+ 30 4.8+4.4 5.8:t:5.2
1.6:t0.7 0.5+0.2 0.5±0.1 0.5±0.1 1.4±0.5
25+2 33±4 59:1:6 51 +4 48± 13
64::1:4 75::t22 67± 16 96:t:4 88+9
levels of petroleum residues, but differed in textural characteristics; and (3) groups IV, VI and VII showed lower petroleum concentrations but differed in other parameters. These results suggest that levels of petroleum residues are not consistently associated with certain sedimentological characteristics, which supports the view that the distribution of petroleum hydrocarbons in sediments of the area is governed mainly by anthropogenic input. The data on sedimentological characteristics provided by Dr S. AI-Abdul Razzaq and colleagues. Dr H. El-Baroudi, Manager, Environmental Science Department, and Dr F. Khalaf, Director, Environmental and Earth Science Division are acknowledged for their support and encouragement.
Kuwait Institute f o r Scientific Research, M. A. Z A R B A Kuwait. O. S. M O H A M M A D V. C. A N D E R L I N I P. L I T E R A T H Y F. S H U N B O
(%)
(%)
Blumer, M. & Sass, J. (1972). Oil pollution: persistence and degradation of spilled fuel oil. Science N. Y, 176, 112(I-1122. Douabul, A. A. Z., AI-Saad, H. T. & Darmoian, S. A. (1984). Distribution of petroleum residues in surficial sediments from Shatt al-Arab river and the north-west region of the Arabian Gulf. Mar. Pollut. Bull., 15, 198-200. Hargrave, B. T. & Phillips, G. A. (1975). Estimates of oil in aquatic sediments by fluorescence spectroscopy. Envir. Pollut., 8, 193-199. lntergovernmental Oceanographic Commission/World Meteorological
Organization(1976). Guide to Operational Proceduresfor the IGOSS Project on Marine Pollution (Petroleum) Monitoring. Manuals and Guides,No. 7. Unesco,Paris. Knap,A. H. & Williams,P.J. (1982). Experimentalstudiesto determine the fate of petroleum hydrocarbons from refinery effluent on an estuarinesystem.Envir. Sci. TechnoL, 16, 1-4. Scarratt, D, J. &Zitko,V.(1972). BunkerC oil in sedimentsand benthic animalsfromshallowdepths in ChedabuctoBay,N.S.J. Fish. Res. Bd Can., 29, 1347-1350. Thomas,M. L. (1973). Effectsof BunkerC oil on intertidaland lagoonal biota in Chedabucto Bay, Nova Scotia. J. Fish. Res. Bd Can., 30, 83-90. Zarba, M. A., Anderlini,V.C., Mohammad,O. S., Literathy,P. & Omar, N. A. (1982).Preliminaryestimateofoil pollutionin marinesediments of Kuwait.K1SR831,KuwaitInstitutefor ScientificResearch,Kuwait.
Marine Pollution Bulletin. Vol.16,No. 5. pp. 211-212. 1985
Primedin GreatBritain
The VD Conspiracy or is there an alternative approach to the treatment of this problem. Sir, The quality (accuracy) of data is a matter which should be close to the heart of all Environmental Scientists and it is quite proper for the subject to be aired in your editorials, as indeed has been done on a number of occasions recently (Hamilton, 1981, 1983 and 1984; Goldberg & Taylor, 1985). In the most recent editorial (Mar. Pollut. Bull., 1985, 16, 1) the authors raise the matter of storage of valid and invalid data in computer banks and the problems that arise when these data are retrieved for evaluation. In seeking a solution to this problem the authors suggest the creation of a system to validate data, as a screening mechanism prior to the entry of the data into the bank(s). They propose that the screening be conducted by a group of mature scientists who have extensive field and laboratory experience and peer group recognition, and that a portion of the finance from funding agencies be set aside
for this purpose. Although this screening process could enable the agencies to identify invalid data and prevent their entry into data banks it will not deal with the basic problem of how one improves the quality of data, i.e., the expert group will treat the symptoms of the 'disease' rather than eradicating the root cause of the problem. I believe that we need more support and finance for quality assurance (QA) work referred to by the authors. A well designed QA programme will not only deal with the analytical aspects of environmental measurements, i.e., setting appropriate targets for precision and accuracy and selecting and testing analytical procedures to meet these targets but it will also address the need to obtain representative samples, in terms of time and space, and use reliable preservation and/or storage procedures for samples. In supporting QA work, however, there are a few comments I would like to make concerning its implementation. Firstly, I agree with the authors that certified or standard reference materials (e.g. NBS materials) play an important part in the validation of an analytical method provided that the materials used are relevant in terms of the matrix and analyte concentration of the samples under investigation in the environmental study. Far too many investigators attempt to validate their analytical procedure with inappropriate reference material, e.g., 211
pies of water were collected at depths of 1, 5, 10, 15.20, 30 and 50 m. using Nansen reversing water samplers. The sampling was done during 1981-1982. Measurements of inorganic nutrients were made by methods described by Friligos ( 1982). The total nutrient in the two gulfs was determined for three periods (Tables 1, 2). The approximate volume in the Kavala Gulf is 5137 × 10 ~' m -~ and in the Alexandroupolis Gulf (less deep) 3376 × 106 m 3. The current levels of the circulatory nutrients were estimated by computing mean values station by station and combining these to give mean values. The mean values were multiplied by the appropriate volumes to give quantitive TABLE 2 Nutrient concentrations in the Kavala Gulf Water column averages (gg-at 1-I) PO4-P SiO4-Si NH3-N NO2-N NO~-N
Date
)~N
March 81 August 81 March 82
0.34 0.18 0.13
2.86 1.07 1.54
0.23 0.49 0.36
0.06 0.12 0.06
0.89 0.52 1/.37
1.18 1.13 0.79
Background*
0.12
1.22
0.36
0.16
0.42
0.94
Total nutrients by cruise (g-at × 10 ") March 81 August 81 March 82
1.75 0.93 0.67
14.70 5.50 7.92
1.18 2.52 1.85
0.31 0.62 0.31
4.57 2.67 1.90
6.06 5.81 4.06
Background*
0.62
6.27
1.85
0.82
2.16
4.83
estimates of total nutrients contained in the basins. The mean values for the Aegean calculated in the same way (Friligos, 1981 Table 3) were taken as a basis for comparison. The tendency of the water of the two gulfs to accumulate nutrients above the background level is shown more clearly in Tables 1, 2, where the data have been converted to ratios of total nutrient to background level. Alexandroupolis Gulf contained three times as much silicate and six times as much nitrate than the background, owing to the contribution of the Evros River. Kavala Gulf phosphate levels are twice background, owing mainly to the presence of a fertilizer factory there. However, the nutrient enrichment in the two areas was smaller that that in Elefsis Bay, which is the most industrialized area in Greece, polluted by sewage and industrial effluents and the water of which remain stagnant in summer. Friligos (1981), reported that the Eiefsis Bay contained nine times as much inorganic nitrogen as the same background. This was due mainly to ammonium being 15 times as high as the background value. Nitrate and nitrite were in quantities greater by 7 and 3 times respectively above background, phosphate and silicate were, respectively, about 5 and 4 times above background.
Institute of Oceanographic, and Fisheries Research, Hellenikon, Athens, Greece
N. FRILIGOS
Ratios of total nutrient per cruise to background nutrient March 81 August 81 March 82 Overall means
2.82 1.50 1.80 1.80
2.34 0.88 1.26 1.49
0.64 1.36 1.00 1.00
0.38 0.76 0.38 0.51
2.12 1.24 0.88 1.41
1.25 1.20 0.84 1.10
*Value obtained by multiplying background concentrations by volume of basin under consideration.
Marine PollutionBulletin, Vol.16, No. 5, pp. 2119-211,1985 Printedin GreatBritain
Petroleum Residues in Surface Sediments of Kuwait The local marine environment of Kuwait is exposed to a relatively high chronic input of petroleum hydrocarbons from industrial effluents, sewage and oil spills. Significant anthropogenic input is also due to the heavy oil shipping activities in the small semi-enclosed water body of the Arabian Gulf. Official statistics of Kuwait showed that 69 t crude oil was accidentally spilled in 1979, during which period 106 million t crude oil was loaded. However, this figure may rise to several times as much due to unreported spillage and the input from urban runoff. Experimental evidence suggests that about 56% of spilled oil becomes adsorbed to bottom sediment (Knap & Williams, 1982) where oxidation may take several years (Scarratt & Zitko, 1972; Blumer & Sass, 1972; Thomas, 1973). Thus the degree of oil pollution in the marine environment may be more accurately assessed by measuring oil in sediments rather than in the overlying water column.
Friligos, N. (1981). Enrichment by inorganic nutrients and oxygen utilization rates in Eiefis Bay 11973-1976). Mar. Pollut. Bull., 12, 431-436. Friligos, N. (1982). Some consequences of the decomposition of organic matter in Elefis Bay, an anoxic basin. Mar. Pollut. Bull. 13, 103-106. Therianos, A. D. 11973). The geographical distribution of river water supply in Greece (in Greek). Bull. Geol. Soc. Greece, XI, 25-28.
01125-326X/85 $3.00+0.1)11 ¢) 1985 PergamonPressLtd.
This study provides background information about the distribution of petroleum hydrocarbons in the coastal and offshore sediments of Kuwait prior to the Norwuz oil spill, against which future impacts can be compared. Samples of surface sediment were collected from 66 locations within the territorial waters of Kuwait by Van Veen grab sampler between November 1979 and December 1980. Aliquots of approx. 2 g freeze-dried sediment were extracted in cyclohexane and analysed for hydrocarbons using Turner 430 spectrofluorometer. The procedure was based on that adopted for the IGOSS Project (IOC/WMO, 1976). The fluorescence intensities were measured at 374 nm (excitation at 310 nm) as recommended by Hargrave & Phillips (1975). Measurements were made against API Kuwait crude oil as an arbitrary standard for comparison. Coefficients of variation for replicate analyses of three sediment samples with differrent levels of petroleum hydrocarbons were 13.4, 8.9, and 10.8%. Concentrations of petroleum residues in sediment samples ranged from 1 to 291 gg g-~ dry wt Kuwait crude oil equivalents. However, concentrations exceeding 100 209
IRAQ
BUB]:]:sY,AN
%
t*
.
/" % .
•:.. :~'.....
J,
ppm hydrocarbons = '~
~ 2.0
At Finta! Fi~
~
2.l-IO.O
AL A, Abroad Astt-
~10.1-2.0
Sht'~aibal" ,
Ol~QI I Q
20. I- 35.0 ~
;,lO0.O
PConc. 35-1OO pDrn is not 0
6
12
18 k m
~o
% 2fl •
~o
KUWAIT 24 °
Fig. 1 Distribution of petroleum residues in marine surface sediments.
gg g-t were observed only in five samples from two areas (Fig. 1): (1) the nearshore area opposite to Ahmadi, Shuaiba and Mina Abdulla ports, and (2) the offshore area south of Qaru Island. Concentrations decreased between these two areas, suggesting that oil pollution possibly originated from two different sources: the first from the refineries and ports area, and the second from the offshore drilling and production of oil and/or from natural seeps (Zarba et aL, 1982). Similar conclusions were reached by Douabul et aL (1984) while discussing distribution of petroleum hydrocarbons in surficial sediments from Iraq. The majority of concentrations ranged from 1 to 35 pg g-t, which is comparable to data reported from a nearby region (Douabul et aL, 1984). The lowest hydrocarbon concentration ( < 2 ~tgg- t) were found in the muddy sediments from the turbid shallow waters south of Bubiyan 210
Island and around Failaka island (Fig. 1). Sediment samples from two locations north of Bubiyan Island showed higher levels (12.0 and 13.8 lag g-~) which may be due to oil refinery activities in Iraq and perhaps the maintenance dredging of Khor Abdulla, as suggested by Douabul et al. (1984). The sedimentological charateristics (determined by another research group in our institute) and data on petroleum hydrocarbons were used to cluster the sediment samples in order to investigate possible association between the two sets of data. Ward's Minimum Variance Hierarchical Method was used with data standardization (SAS Library). This analysis divided the samples into seven groups, the characteristics of which are summarized in Table 1: (1) groups II and III showed very high levels of petroleum hydrocarbons, but they differed in all other parameters; (2) groups I and V showed moderate
Volume 16/Number 5/May 1995 TABLE 1
Summary of characteristics of groups formed by cluster analysis Petroleum hydrocarbons (cagg-')
TOC (%)
Average +S.D. CaCO ~
< 63 camfraction
Group No.
No. of observations
I II
6 2
13::I:13 241:1:71
0.7+0.5 0.7+0.1
75+ 8 55=t I
8+4 9±0
III IV V VI VII
2 8 10 25 11
1145:8.5 4.5+4.9 16+ 30 4.8+4.4 5.8:t:5.2
1.6:t0.7 0.5+0.2 0.5±0.1 0.5±0.1 1.4±0.5
25+2 33±4 59:1:6 51 +4 48± 13
64::1:4 75::t22 67± 16 96:t:4 88+9
levels of petroleum residues, but differed in textural characteristics; and (3) groups IV, VI and VII showed lower petroleum concentrations but differed in other parameters. These results suggest that levels of petroleum residues are not consistently associated with certain sedimentological characteristics, which supports the view that the distribution of petroleum hydrocarbons in sediments of the area is governed mainly by anthropogenic input. The data on sedimentological characteristics provided by Dr S. AI-Abdul Razzaq and colleagues. Dr H. El-Baroudi, Manager, Environmental Science Department, and Dr F. Khalaf, Director, Environmental and Earth Science Division are acknowledged for their support and encouragement.
Kuwait Institute f o r Scientific Research, M. A. Z A R B A Kuwait. O. S. M O H A M M A D V. C. A N D E R L I N I P. L I T E R A T H Y F. S H U N B O
(%)
(%)
Blumer, M. & Sass, J. (1972). Oil pollution: persistence and degradation of spilled fuel oil. Science N. Y, 176, 112(I-1122. Douabul, A. A. Z., AI-Saad, H. T. & Darmoian, S. A. (1984). Distribution of petroleum residues in surficial sediments from Shatt al-Arab river and the north-west region of the Arabian Gulf. Mar. Pollut. Bull., 15, 198-200. Hargrave, B. T. & Phillips, G. A. (1975). Estimates of oil in aquatic sediments by fluorescence spectroscopy. Envir. Pollut., 8, 193-199. lntergovernmental Oceanographic Commission/World Meteorological
Organization(1976). Guide to Operational Proceduresfor the IGOSS Project on Marine Pollution (Petroleum) Monitoring. Manuals and Guides,No. 7. Unesco,Paris. Knap,A. H. & Williams,P.J. (1982). Experimentalstudiesto determine the fate of petroleum hydrocarbons from refinery effluent on an estuarinesystem.Envir. Sci. TechnoL, 16, 1-4. Scarratt, D, J. &Zitko,V.(1972). BunkerC oil in sedimentsand benthic animalsfromshallowdepths in ChedabuctoBay,N.S.J. Fish. Res. Bd Can., 29, 1347-1350. Thomas,M. L. (1973). Effectsof BunkerC oil on intertidaland lagoonal biota in Chedabucto Bay, Nova Scotia. J. Fish. Res. Bd Can., 30, 83-90. Zarba, M. A., Anderlini,V.C., Mohammad,O. S., Literathy,P. & Omar, N. A. (1982).Preliminaryestimateofoil pollutionin marinesediments of Kuwait.K1SR831,KuwaitInstitutefor ScientificResearch,Kuwait.
Marine Pollution Bulletin. Vol.16,No. 5. pp. 211-212. 1985
Primedin GreatBritain
The VD Conspiracy or is there an alternative approach to the treatment of this problem. Sir, The quality (accuracy) of data is a matter which should be close to the heart of all Environmental Scientists and it is quite proper for the subject to be aired in your editorials, as indeed has been done on a number of occasions recently (Hamilton, 1981, 1983 and 1984; Goldberg & Taylor, 1985). In the most recent editorial (Mar. Pollut. Bull., 1985, 16, 1) the authors raise the matter of storage of valid and invalid data in computer banks and the problems that arise when these data are retrieved for evaluation. In seeking a solution to this problem the authors suggest the creation of a system to validate data, as a screening mechanism prior to the entry of the data into the bank(s). They propose that the screening be conducted by a group of mature scientists who have extensive field and laboratory experience and peer group recognition, and that a portion of the finance from funding agencies be set aside
for this purpose. Although this screening process could enable the agencies to identify invalid data and prevent their entry into data banks it will not deal with the basic problem of how one improves the quality of data, i.e., the expert group will treat the symptoms of the 'disease' rather than eradicating the root cause of the problem. I believe that we need more support and finance for quality assurance (QA) work referred to by the authors. A well designed QA programme will not only deal with the analytical aspects of environmental measurements, i.e., setting appropriate targets for precision and accuracy and selecting and testing analytical procedures to meet these targets but it will also address the need to obtain representative samples, in terms of time and space, and use reliable preservation and/or storage procedures for samples. In supporting QA work, however, there are a few comments I would like to make concerning its implementation. Firstly, I agree with the authors that certified or standard reference materials (e.g. NBS materials) play an important part in the validation of an analytical method provided that the materials used are relevant in terms of the matrix and analyte concentration of the samples under investigation in the environmental study. Far too many investigators attempt to validate their analytical procedure with inappropriate reference material, e.g., 211