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Organic Contaminants in Adult Aquatic Insects of the St. Clair and Detroit Rivers, Ontario, Canada
J. Great Lakes Res. 14(2):148-156 Internat. Assoc. Great Lakes Res., 1988
ORGANIC CONTAMINANTS IN ADULT AQUATIC INSECTS OF THE ST. CLAIR AND DETROIT RIVERS, ONTARIO, CANADA
Jan J. H. Ciborowski and Lynda D. Corkum Department of Biological Sciences University of Windsor Windsor, Ontario N9B 3P4 ABSTRACT. Night-flying Trichoptera and Ephemeroptera were attracted using long-wave ultraviolet light and collected from 8 Canadian sites adjacent to the St. Clair and Detroit rivers. Gas chromatographic analysis of the extracts from 40 samples of the insects revealed significant concentrations ofpentachiorobenzene (QCB), hexachlorobenzene (HCB), octachlorostyrene (OCS), and 16 polychlorinated biphenyl (PCB) congeners in almost all animals collected. Principal component analysis accounted for 84 % of variation in contaminant concentration among samples. The principal components (PCs) correlated highly with concentrations of 9 hexa-, hepta-, and octachlorobiphenyls (PC-I,' 46% ofoverall variation), 4 tetra- and pentachlorobiphenyls (PC-II; 17% of variation), QCB, HCB, and OCS (PC-III,' 8%), and 2 trichlorobiphenyls (PCs IV and V; each 6% of variation). Values of PC-I were significantly greater among Detroit River than among St. Clair River samples. Values of PC-II were highest for samples from upstream stations on the two rivers. Values of PC-III were higher for St. Clair River samples than for Detroit River samples. These trends are consistent with patterns observed in other biota and sediment previously collected from equivalent sites. Contaminant levels also varied among taxa collected from the same site, possibly because of different larval feeding habits or microdistribution, or adult flight ability. Collection of adults has potential as an inexpensive alternative to aquatic sampling methods in surveys of biota for organic contamination. ADDITIONAL INDEX WORDS: Toxic substances, chlorinated hydrocarbons, Ephemeroptera, Trichoptera.
INTRODUCTION
effort. Although molluscs can be retrieved and analysed individually, they may occur sporadically and in low densities. Diver-assisted collection alleviates some sampling problems, but poor visibility, strong currents, and hazards associated with commercial shipping traffic render certain habitats inaccessible. Ephemeroptera (mayflies) and Trichoptera (caddisflies) pass most of their lives as aquatic larvae, during which time feeding and benthic movements bring them into intimate contact with suspended and deposited sediments. The winged adults are largely nocturnally active, at which time they disperse, mate, and the females oviposit. Many species are attracted to lights, sometimes in enormous numbers. This is a common summer phenomenon at locations along the St. Clair and Detroit rivers. These rivers have been designated Areas of Concern (International Joint Commission 1985) because of extensive organic contami-
Recent research has increasingly stressed the importance of benthic invertebrates as agents of contaminant transfer between sediments and higher trophic levels in freshwater aquatic systems. Larsson (1984) showed that larval Chironomidae could accumulate significant levels of PCBs from contaminated sediments. Oliver (1984) reported similar capabilities for oligochaete worms. The tendency of bivalve molluscs to selectively accumulate toxic organic compounds has stimulated research to assess their potential utility as biomonitors (Pugsley et al. 1985, Kauss and Hamdy 1985). Investigation of invertebrate contamination in aquatic habitats has been hindered by the difficulties of obtaining samples efficiently, especially in large rivers. Aquatic annelids and larval insects are abundant in both lentic and lotic habitats, but separating organisms from the sediments with which they are collected requires expertise and intensive
148
149
ORGANIC CONTAMINANTS IN AQUATIC INSECTS TABLE1. Location of 1986 sample stations and sunset weather conditions. (DR River, DC = overcast).
= Detroit River, SCR = St.
Clair
Stn.
River
Designation
Latitude (North)
Longitude (West)
Date
(0C)
Sky
Wind (km h- 1)
1 2 3 4 5 6 7 8
DR DR DR DR SCR SCR SCR SCR
Amherstburg R. Canard Windsor A Windsor B Port Lambton Sombra Corunna Sarnia
42°06'01" 42°11'48" 42°18'23" 42°20'27" 42°38'38" 42°45'04" 42°53'26" 42°58'26"
83°06'47" 83°06'13" 83°04'27" 82°56'56" 82°30'14" 82°27'54" 82°27'15" 82°24'32"
5 July 6 July 7 July 9 July 14 July 16 July 15 July 10 July
24 28 24 22 21 22 24 17
high OC hazy high OC clear clear hazy high OC high OC
W 2-5 calm calm calm calm E 2-5 S 2-5 NW 2-5
nant accumulation resulting from release of industrial effluents. The objectives of our study were to determine if adult insects that have emerged from aquatic habitats might be useful as a biomonitoring tool and a cost effective alternative to sampling organisms directly within the aquatic environment. We wished to evaluate whether enough adults, attracted with longwave ultraviolet light, could be collected to permit analysis for organic contaminants, and whether samples from sites on the S1. Clair and Detroit rivers harbored significant contaminant levels. METHODS Sample Collection Adults of aquatic insects were captured at eight Canadian sites approximately 8 km apart along the Detroit and S1. Clair rivers between 4 and 16 July 1986 (Table 1). Stations were selected within 30 m of the east riverbank that provided a clear view of the river. Sampling was conducted on warm, relatively calm evenings from near sunset (2130 h EDT) until approximately 2300 h EDT (Table 1). A white cotton sheet, which served as a light reflector and as a substrate for insects, was placed over an automobile hood. Adults were attracted using a 12V115W DC fluorescent long-wave ultraviolet (UV) lamp (length, 45 cm) placed on the sheet and powered from the automobile battery. Mode of collection varied with taxa. Adult Trichoptera were captured using hexane-rinsed 500-mL amber glass jars. Jar lids had a hole cut into their center to accommodate the narrow end of a 12.S-cm dia. funnel. Insects were guided onto the inner surface of the funnel and tapped into the
Temp.
jar. Several g of dry ice within the jar both anaesthetized and cooled trapped insects. Hexagenia (Ephemeroptera) adults that alighted on the sheet were grasped by the wings and placed in amber jars containing dry ice. Upon completion of sampling, the sheet was quickly folded to retain insects that had not been individually captured and transported to the laboratory in a cooler containing dry ice. All organisms were stored overnight in a freezer at -20°C prior to processing. Sample Processing The small size of the insects necessitated pooling organisms prior to analysis. The number of animals comprising a sample depended upon both individual size and quantities collected. In the laboratory, animals were sorted into precleaned glass containers using hexane-rinsed forceps. Although many taxa were attracted to the UV light and incidentally captured, only four were sufficiently widespread and abundant to be used for contaminant analysis. We retained mayflies (Hexagenia and Caenis) and caddisflies (Macronema and "others"). "Other" caddisflies consisted of animals of size and coloration predominant at a particular site; unusual specimens were not included. Trichoptera were sorted without the aid of magnification by summer assistants having minimal entomological training. Preliminary weighing of individuals of each taxon at each site was conducted to estimate numbers adequate for a sample. We attempted to divide animals evenly to produce at least two replicates, each of a total fresh weight between 2 and 6 g. A subsample of organisms was taken from each replicate for further taxonomic analysis (including up to 100 "other" caddisflies per site, as
150
CIBOROWSKI and CORKUM
available) and biomass determination. Samples for contaminant analysis were stored at -20°C for up to 6 weeks prior to extraction. Animals used for biomass determination were weighed singly (Macronema, Hexagenia) or in groups of 6 (other Trichoptera) or 25 (Caenis) to the nearest 0.1 mg on a Sartorius model 2462 balance immediately after sorting, and again after drying at 60°C for 24 h. Sample biomasses were estimated by multiplying the number of animals in a sample by the mean dry weight of animals in the corresponding biomass subsample. Extraction and Contaminant Analysis Analysis for contaminants was performed by the Great Lakes Institute analytical laboratory, University of Windsor, following methods outlined by Pugsley et af. (1985). Samples were placed in 120 mL of acetonitrile with 40 mL water and homogenized for 1-1.5 min with a polytron blender. The fluid was filtered under vacuum through a sintered glass funnel and placed in a separatory funnel. The homogenization/filtration procedure was repeated once using 50 mL of fresh acetonitrile, and twice more with 20-mL lots of acetonitrile. One mL of concentrated sulphuric acid was added to hydrolyze lipids. The filtrate was then extracted by shaking for 2 min with a 150 mL portion and then two 75 mL portions of petroleum ether. The petroleum ether extract was washed with 200 mL of water and then dried by passage through a column containing 15 g of anhydrous sodium sulphate. Samples were cleaned up by passage through 20 mm x 40 cm glass columns containing 1-2 cm of anhydrous sodium sulphate over 20 g of Florisil, eluted with 200 mL of petroleum ether, and then concentrated to 5 mL with a Kuderna-Danish evaporator. Contaminant extracts were analyzed by injection of 1-p.L samples into a Hewlett-Packard model 5790A gas chromatograph (GC) equipped with a 25 m x 0.25 mm fused silica column (J & W Scientific) and an electron capture detector. Splitless injection mode was used at an injector temperature of 250°C. The column was temperature programmed for 0.5 min at 50°C, heated to 250°C at 2°C min- 1 and held for 20 min at 250°C. Detector temperature was 300°C. Helium carrier gas was delivered at a rate of 1.5 mL min-I. Detector makeup gas consisted of 5070 methane-95% argon at 35 mL min-I. Peak areas of contaminants and standards were measured with a Hewlett-Packard
model 3390A integrator. A blank analysis was conducted with each analytic series (2-5 randomly selected samples). Contaminants were quantified against a standard mixture consisting of octachlorostyrene (OCS), pentachlorobenzene (QCB), and hexachlorobenzene (HCB), each at 5.0 p.g kg-I, and Aroclors 1242, 1254, and 1260, each at 20 p.g kg-I. Identification and quantification of 16 PCB congeneric constituents (see Table 3) was based on peak patterns, relative retention times, and relative composition of Aroclors as presented by Tuinstra and Traag (1983). Because relative composition of congeners in Aroclors can vary from lot to lot, concentrations of PCBs presented are tentative and must be regarded as relative rather than absolute; however, the data are admissible for comparative purposes among samples. Analysis of blind samples for total PCBs produces results within 5% of true values (1986 International Joint Commission Quality Assurance Program). Equipment failures necessitated refrigerating some extracted samples for up to 18 d prior to GC analysis. This introduced substantial variation to replicates (stored samples had higher apparent concentrations of contaminants due to solvent evaporation). To evaluate this, relative concentration of each sample (Y/Y, where Y is the mean of all replicates of one taxon at one station) was regressed against storage time for each of the contaminants examined. Significant relationships (p < 0.01) between relative concentration and storage time were found for 11 of 19 compounds (maximum R2 = 0.39, overall median R2 = 0.22). Accordingly, values of each contaminant were statistically adjusted to a standard storage time according to the derived regression equations (Sokal and Rohlf 1969, pp. 444-445). This procedure reduces the variance among replicates taken as a group, without affecting the mean value of these replicates. Insufficient material was available to permit assessment of recovery efficiency or insect lipid content. Recovery efficiencies for our system using bivalve tissues average 70-85% for HCB, OCS, QCB, and total PCBs (Pugsley et af. 1985; unpublished data). Calculations were not corrected for procedural losses. Statistical Analyses Concentrations of many of the compounds were highly correlated with one another among repli-
151
ORGANIC CONTAMINANTS IN AQUATIC INSECTS cates, taxa, and sites. Consequently, principal component analysis (PCA; Dixon and Brown 1979) was used to reduce the data set prior to further statistical analysis. Concentrations were Ln(Y + 1) transformed prior to analysis. Following the PCA analysis, we determined the degree of association between the original 19 variables (compounds) and the derived principal components using Spearman's rank correlation coefficient (Sokal and Rohlf 1969). Analyses of variance (ANOVA, unbalanced hierarchical design; SAS Institute Inc. 1985) were then used to test for differences in values of the principal components among rivers and sites for each taxon, and also pairs of taxa occurring at common sites. Significant differences detected among principal components scores imply equivalent differences in the concentrations of the contaminants associated with each component. RESULTS A total of 40 samples was analyzed for PCBs and three other organochlorine compounds, of which one sample was strongly deviant from replicates and was discarded. Adults of Trichoptera were the only organisms collected at all stations. The caddisfly Macronema zebratum Hagen (Hydropsychidae), whose larvae are filter-feeders, comprised the entire Trichoptera collection at Amherstburg. Samples of Trichoptera from other stations were also dominated by genera of hydropsychid net-spinning caddisflies; primarily Cheumatopsyche spp (Table 2). Leptoceridae were the only other caddisflies commonly collected. They dominated samples at Port Lambton. Mayflies, Caenis (primarily C. latipennis Banks) and Hexagenia (mostly H. limbata (Serville», were each collected at four stations. Overall abundance of flying adults was much reduced at the three upstream sites of the St. Clair River. This was reflected in the reduced number of replicates analyzed from these areas. All taxa at all sites contained detectable levels of both PCBs and other organochlorine compounds (Table 3). Five principal components accounted for 84070 of the variation in contaminant concentrations among samples. The first principal component (PC-I) accounted for 46% of overall variation and was highly positively correlated with concentrations of nine PCB congeners (primarily hexa-, hepta-, and octachlorobiphenyls) and negatively correlated with HCB concentration (Table 4). PC-II explained an additional 17070 of variation
TABLE 2. Relative taxonomic composition (percent) of "other" Trichoptera used in contaminant analysis. Figures in bold face are family totals. All specimens collected at station 1 were Macronema zebratum (Hydropsychidae). Taxon
1
2
3
STATION 4 5 6
Hydropsychidae 100 70 84 94 Cheumatopsyche spp 64 76 94 Hydropsyche spp 6 7 1 Potamyia sp. 0 0 0 Lepidostomatidae Lepidostoma sp. 30 16 6 Leptoceridae Ceraclea spp - 21 16 4 Mystacides spp Oecetus spp 8 1 - Triaenodes sp. Unidentified 1 0 0 0 Molannidae Molanna sp. 0 0 0 Polycentropodidae Neureclipsis sp. Polycentropus sp. - - NA 100 100 103 Total No. examined
7
8
36 65 98 98 27 52 82 94 9 13 16 4 0 13 13 59 22 16 13 4 30 9 9 1 0 0
-
5 I
0
-
0
-
0 -
2
1 1
-
2 0 0
1 1 0
-
4 70 23 99 100
and was associated with five tetra- and pentachlorobiphenyls. Three contaminants, QCB, HCB, and OCS, were positively correlated with values of PC-III, which accounted for 8% of overall variation. PC-IV and PC-V were each highly correlated with a different trichlorobiphenyl and each removed an additional 6% of variation. Spatial trends in contaminant concentrations were evident for all taxa, and these patterns are reflected in site-to-site variation in mean principal component scores (Fig. 1). Detroit River samples of Trichoptera (stations 1-4, Table 3) had high concentrations of highly chlorinated PCBs (PCBs associated with PC-I) and relatively low non-PCB organochlorine concentrations. Maximum concentrations of each of the PCB congeners (except PCB 18) were recorded in Trichoptera from the two Windsor stations (stations 3 and 4, Table 3). Mean values of PC-I for Detroit River Trichoptera were significantly greater than values for the St. Clair River (Fig. lA; p < 0.01). In contrast, Trichoptera collected from the St. Clair River (stations 5-8, Table 3) had significantly higher QCB, OCS, and especially HCB concentrations than their Detroit River counterparts. This was reflected in significant differences in mean scores of PC-III (Fig. lC; P < 0.01). Significant variation was also evident among trichopteran samples collected from upstream versus
10-0 CIt
N
TABLE 3.
Mean (and S.E.) concentration of organic contaminants (p.g kg-I dry weight) in aquatic insect taxa among stations. CONTAMINANT
Stn.
Taxon
1 Macronema
No. -1 Dry sample WI. (g) N 150 1.9328
5
QCB
HCB
OCS
PCB 18
3.99 (1.497)
32.94 (2.811)
42.98 (3.601)
0.06 (0.057)
10.75 NA
21.18 NA
PCB 28
PCB 52
PCB 66
PCB 87
PCB 95
PCB 97
PCB 101
PCB 118
PCB 138
PCB 141
PCB 153
PCB 170
PCB 180
PCB 187
PCB 194
1.98 (0.435)
3.75 (0.471)
20.4 (2.472)
2.84 (0.399)
7.77 (1.581)
1.86 (0.204)
19.02 (5.853)
13.80 (3.066)
25.71 (2.991)
2.97 (1.401)
29.25 (3.732)
6.30 (3.366)
22.80 (3.360)
12.33 (1.242)
3.78 (1.152)
1.50 NA
1.92 NA
10.44 NA
15.78 NA
27.33 NA
2.25 NA
35.52 NA
22.62 NA
34.02 NA
17.49 NA
12.81 NA
8.55 NA
Macronema
108
Trichoptera (Other)
500 0.8958 3
1.28 (0.648)
19.51 (1.844)
36.21 (4.647)
0.63 (0.543)
2.01 (0.660)
9.60 (2.772)
19.17 (4.503)
6.30 (1.767)
23.88 (6.600)
4.05 (0.873)
25.74 (6.882)
30.48 (7.833)
45.06 (12.138)
9.96 (3.564)
48.84 (12.882)
11.40 (6.108)
37.41 (12.144)
20.13 (5.493)
4.11 (1.212)
1.2536 2
2.24 (0.310)
25.54 (4.776)
10.47 (0.185)
0.57 (0.750)
1.83 (0.510)
8.58 (2.466)
15.30 (2.124)
5.10 (1.017)
13.56 (1.587)
4.29 (0.933)
14.37 (4.554)
13.65 (4.257)
19.62 (3.543)
1.35 (1.347)
20.64 (4.758)
1.35 (0.078)
9.27 (3.084)
5.52 (1.362)
0.84 (0.846)
3
1.50 (0.274)
15.65 (2.376)
35.79 (3.992)
0.87 (0.471)
2.67 (1.581)
12.75 (3.888)
23.64 (3.717)
8.79 (1.377)
29.22 (1.575)
5.07 (0.831)
38.22 (4.935)
46.32 (10.095)
62.25 (11.694)
19.59 (4.146)
76.56 (15.462)
24.24 (7.143)
70.02 (15.549)
36.27 (6.798)
12.12 (1.632)
2000 0.7200 2
1.16 (1.162)
21.88 (1.705)
17.54 (0.126)
0.72 (0.708)
6.18 (0.279)
8.16 (8.151)
32.82 (1.377)
10.08 (0.384)
32.70 (1.611)
6.63 (0.330)
28.89 (0.627)
23.91 (0.174)
42.33 (2.193)
9.78 (1.086)
37.59 (0.027)
6.87 (6.858)
19.26 (0.228)
17.67 (3.900)
2.13 (0.219)
Caenis Trichoptera (Other)
Caenis
1850 550
1.1718
1.1568
l'
<0.49 NA
<0.09 NA
2.28 NA
<3.84 NA
1.56 NA
..=
n 0
:=
600
1.1111
4
2.65 (0.382)
20.77 (1.588)
40.94 (9.069)
0.84 (0.195)
2.01 (0.726)
11.88 (1.797)
22.44 (3.027)
10.38 (1.608)
24.84 (0.480)
6.39 (1.077)
30.48 (4.188)
35.04 (17.619)
62.64 (6.933)
11.01 (1.950)
59.34 (16.050)
14.28 (5.736)
55.14 (11.271)
24.45 (5.352)
4.95 (1.347)
~
Hexagenia
110
1.2578
3
9.48 119.25 (0.750) (7.746)
17.33 (1.469)
0.09 (0.092)
0.27 (0.261)
4.92 (0.738)
10.23 (1.554)
2.94 (0.504)
11.49 (0.927)
3.21 (0.432)
8.34 (2.313)
9.09 (2.034)
16.65 (0.600)
3.03 (1.065)
18.45 (2.835)
3.09 (1.590)
10.53 (2.361)
5.34 (0.756)
2.16 (1.140)
~
Trichoptera (Other)
375 0.9222
2
2.84 (1.134)
0.36
6.95 (3.498)
8.10 (0.945)
4.68 (1.230)
4.17 (1.266)
2.34 (1.095)
18.18 (14.580)
11.91 (3.480)
20.88 (4.578)
1.68 (0.078)
18.39 (4.962)
4.17 (4.179)
12.51 (4.080)
4.74 (0.027)
4 Trichoptera (Other)
Caenis Hexagenia 6 Trichoptera (Other)
Caenis Hexagenia Trichoptera
3750
1.2747 3
120 2.0274 2
Hexagenia
16.Q7 222.68 253.32 (1.077) (24.677) (17.454)
0.30 (0.366)
0.06 (0.042)
2.55 (2.541)
19.29 (2.709)
27.30 5.76 (2.886) (14.061)
4.68 (0.351)
17.28 (1.656)
15.03 (2.010)
20.13 (1.584)
1.14 (0.288)
16.98 (1.644)
0.12 (0.108)
6.27 (1.242)
3.72 (0.804)
0.36 (0.219)
n
1.50 (0.211)
0.18 (0.009)
0.36 (0.001)
4.14 (1.836)
9.21 (1.569)
1.92 (0.024)
8.49 (3.357)
1.41 (0.027)
5.40 (0.273)
4.35 (0.336)
6.00 (0.495)
0.57 (0.084)
8.01 (0.723)
3.63 (1.701)
4.35 (0.900)
1.68 (0.420)
0.93 (0.051)
~~
31.35 (7.229)
6.10 (1.514)
1
3.73 NA
45.28 NA
261.19 NA
2.73 NA
<0.15 NA
7.56 NA
14.64 NA
6.69 NA
8.28 NA
3.57 NA
17.79 NA
7.05 NA
27.06 NA
2.34 NA
18.60 NA
<0.33 NA
36.60 NA
4.44 NA
5.85 NA
1000
1.0650
1
6.23 NA
84.95 NA
97.98 NA
0.15 NA
0.06 NA
8.19 NA
13.05 NA
4.32 NA
23.88 NA
2.97 NA
11.61 NA
9.30 NA
11.31 NA
0.60 NA
9.93 NA
<0.15 NA
2.94 NA
2.16 NA
0.63 NA
82
1.3962
I
3.70 NA
133.30 NA
36.22 NA
0.48 NA
0.90 NA
3.30 NA
10.65 NA
3.48 NA
8.46 NA
2.58 NA
15.33 NA
10.05 NA
16.20 NA
1.68 NA
19.17 NA
7.23 NA
9.51 NA
3.96 NA
<0.21 NA
3.48 (3.474)
13.05 (1.221)
5.31 (1.794)
<0.24 NA
4.89 (1.221)
2.49 (2.496)
0.54 (0.318)
15.78 (0.579)
6.24 (1.080)
5.49 (0.180)
500
1.2450 2
2.06 (0.105)
40.42 181.07 (0.004) (31.434)
0.69 (0.267)
0.72 (0.306)
3.69 (0.348)
14.64 (4.092)
5.46 (0.777)
13.20 (6.255)
3.18 (0.387)
14.25 (1.659)
9.36 (1.338)
25.98 (3.300)
2.61 (1.113)
18.27 (2.052)
325
1.2144 2
21.37 187.27 415.40 (3.072) (27.591) (100.029)
0.54 (0.726)
0.66 (0.660)
16.05 (10.698)
20.43 (4.965)
33.27 9.81 (4.959) (23.688)
6.12 (2.175)
28.80 (13.380)
18.42 (8.514)
16.95 (0.174)
1.35 (1.338)
14.79 (0.603)
67
0.8546 2
2.62 (2.617)
8.46 (0.619)
8.76 (2.218)
6.24 (0.795)
15.03 (7.425)
6.33 (1.920)
23.49 (1.920)
14.94 (0.741)
21.03 (1.692)
4.89 (0.987)
37.53 (2.238)
• 1 replicate discarded.
~
~0.351)
0.63 (0.630)
0.4783
(Other)
00
48.48 147.19 (8.140) (39.937)
175
(Other) Trichoptera
<0.30 NA
..
18.63 <0.41 (2.049) NA
<0.15NA
<0.09 NA
<0.12 NA 5.85 (4.347)
=-=
0
ORGANIC CONTAMINANTS IN AQUATIC INSECTS TABLE 4.
153
Correlation between concentration 0/ organic contaminants and principal components.
Principal Component Compound Designation 1 PC-I PC-II PC-III PC-IV PC-V 2,2',3,4,4',5,5'-Heptachlorobiphenyl PCB 180 -0.191 0.183 0.216 0.889** 0.151 2,2',4,4',5,5'-Hexachlorobiphenyl PCB 153 -0.171 0.233 0.879** 0.328 0.024 2,2',3,4',5,5',6'-Heptachlorobiphenyl PCB 187 -0.214 0.364 0.004 0.842** 0.195 2,2',3,4,4',5'-Hexachlorobiphenyl PCB 138 -0.063 0.319 0.225 0.824** 0.318 2,2',3,3',4,4',5,5'-Octachlorobiphenyl PCB 194 -0.200 -0.061 -0.133 0.824** 0.226 2,2', 3,4,5,5'-Hexachlorobiphenyl PCB 141 0.043 -0.128 0.026 0.805** 0.400 2,3',4,4',5-Pentachlorobiphenyl PCB 118 0.084 0.147 0.093 0.756** 0.457* 2,2',4,5,5'-Pentachlorobiphenyl PCB 101 0.082 0.644** 0.523** 0.086 0.297 2,2',3,3',4,4',5-Heptachlorobiphenyl PCB 170 -0.380 0.073 0.532** 0.124 0.273 2,3',4,4'-Tetrachlorobiphenyl PCB 66 0.430* 0.242 0.454* 0.498* 0.111 2,2' ,3' ,4,5-Pentachlorobiphenyl PCB 97 0.866** 0.048 0.061 0.262 0.144 2,2',3,5',6-Pentachlorobiphenyl PCB 95 0.825** 0.073 0.198 0.163 -0.124 2,2',5,5'-Tetrachlorobiphenyl PCB 52 0.783** -0.114 -0.211 0.155 0.061 2,2',3,4,5'-Pentachlorobiphenyl PCB 87 0.376 0.739** 0.053 0.120 0.448* Pentachlorobenzene QCB 0.091 0.819** -0.135 -0.227 -0.206 Hexachlorobenzene HCB 0.787** -0.217 -0.019 -0.458* -0.239 OCS Octachlorostyrene 0.759** -0.017 -0.108 0.329 0.026 2,4,4'-Trichlorobiphenyl PCB 28 0.018 -0.281 0.900** 0.084 0.247 2,2',5-Trichlorobiphenyl PCB 18 0.269 0.159 0.045 0.847** 0.107 IPCB numbering follows Ballschmiter and Zell 1980. *p
downstream sites within each river. Samples from upstream stations had higher concentrations of 4-, 5-, and 6-chlorine PCBs (those associated with PCII) than occurred in downstream samples (PCBs 52 to 153, Table 3). However, whereas the contrasts for samples from the Detroit River occurred between the two upstream stations (3 and 4) and the two downstream sites (1 and 2), St. Clair River station differences were between the single Sarnia site (8) and the three downstream stations (5, 6, and 7, Table 3). Analysis of variance indicated significant within-river differences among PC-II scores, with which these PCB congeners were highly correlated (Fig. IB; P < 0.05). Values of PC-II did not differ between rivers (p > 0.05). There were no discernable trends in concentration of the two trichlorobiphenyls found in Trichoptera (p > 0.05; Figs. ID and IE). Ephemeroptera tended to have low concentrations of PCBs associated with PC-I relative to Trichoptera from comparable sites (stations 4, 5, 7, and 8, Table 3; Fig. IA). Hexagenia samples from Sarnia (station 8) had higher concentrations of PCBs associated with PC-II (Fig. IB) and lower non-PCB organochlorine concentrations (Fig. IC) than did Hexagenia samples from stations upstream and downstream of Lake St. Clair (sta-
tions 4, 5, and 6). Overall, Trichoptera had significantly higher levels of QCB, HCB, and OCS than did Hexagenia (expressed as mean PC-III values, Fig. IC; p < 0.05). Samples of Caenis varied among sites primarily with reference to QCB, HCB, and OCS concentrations (Table 3). Samples from the St. Clair River (stations 5 and 6) had much higher concentrations of these chemicals than did collections from the Detroit River (stations 2 and 3, Table 3). St. Clair River Caenis in general also had greater concentrations of the three non-PCB compounds than did either Trichoptera or Hexagenia occurring at equivalent sites (p < 0.05; Fig. IC). Caenis samples from the upper Detroit River (station 3) differed from remaining Caenis samples (stations 2, 5, and 6) in having greater levels of highly chlorinated PCBs (associated with PC-I, Fig. IA) and lower concentrations of HCB (Table 3). DISCUSSION To be potentially useful for biomonitoring, naturally occurring organisms should meet several criteria. Taxa should be widespread and accessible across a range of environmental conditions. Samples must provide data sufficiently precise that site-
154
cmOROWSKI and CORKUM 2
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Station FIG. 1. Means (± 1 S.E.) of principal component scores for insect samples collected at various sites on the Detroit and St. Clair rivers. Station numbers correspond to those listed in Table 1. Solid lines and circles, all Trichoptera; dashed lines and open circles, Caenis; open squares, Hexagenia. A: PC-I, correlated with concentrations of PCBs 101, 118, 138, 141, 153, 170, 180, 182, and 194; B: PC-II, correlated with PCBs 52, 66, 87, 95, 97, and 101; C: PC-III, correlated with QCB, HCB, and OCS; D: PC-IV, correlated with PCB 28 and PCB 66; E: PC- V, correlated with PCB 18 and PCB 87.
to-site variation can be discerned with reasonable confidence; and the derived measurements must accurately reflect contaminant patterns of the biota at large. Our study shows that adult aquatic
insects may be easily collected using UV light attraction in numbers adequate for contaminant analysis. Variability in contaminant concentrations was sufficiently low that we could detect significant differences in contaminants among taxa and within single taxa among sites. Note, however, that our "replicates" at sites represent single, large samples that were partitioned in the laboratory. Accordingly, they reflect variation in our subsampling and processing methods rather than on-site environmental variability. Nevertheless, each collection represents an integrated sample of individuals from a potentially extensive surrounding area. Spatial patterns of contamination indicated by our samples appear to correspond with results of other studies of organic contaminants in biota and sediments of the St. Clair and Detroit rivers. Trichoptera were present at all eight sites of both the Detroit and St. Clair rivers; Caenis were collected at two sites on each river; and three of four Hexagenia sites were located on the St. Clair River. Concentrations of highly chlorinated PCBs (hexa-, hepta-, and octachlorobiphenyls) were significantly greater in Trichoptera emerging from Detroit River sites than in samples from St. Clair River sites. Levels of non-PCB organochlorine compounds (QCB, HCB, and OCS) were higher in Trichoptera collected from the St. Clair River than from the Detroit River. Additionally, upstream/ downstream variation in contaminant concentrations was evident in both rivers; greatest concentrations of less highly chlorinated PCBs (tri-,tetra-, and pentachlorobiphenyls) were found in samples from upstream sites. Similar spatial trends were evident among sites for the mayfly, Caenis. Yet concentrations of both PCBs and certain other organochlorides in Caenis differed from levels in the caddisflies. Concentrations of HCB were typically higher in the mayfly taxa than in caddisflies, with the exception of the Sarnia samples, where the trend was reversed. Our detection of elevated OCS concentrations at St. Clair River sites and high PCB levels at upstream Detroit River sites is consistent with assessments of local contamination by earlier workers (e.g., Thornley and Hamdy 1984, Kauss and Hamdy 1985, Pugsley et af. 1985, Struger et af. 1985). Several studies (Frank et af. 1977, Thornley and Hamdy 1984, Kauss and Hamdy 1985, Oliver and Bournbonniere 1985, Smith et af. 1985) cite the Detroit River's western (USA) shore as the major source of PCBs deposited in the western basin of
ORGANIC CONTAMINANTS IN AQUATIC INSECTS
Lake Erie. Thornley and Hamdy (1984) reported sediment total PCB concentrations in excess of Ontario guidelines (50 p.g/kg) for dredging at over 59010 of Detroit River sites that they sampled. Among the Canadian samples they examined, greatest total PCB concentrations occurred within an area that includes our two upstream sites on the Detroit River. Kauss and Hamdy (1985) examined short-term contaminant uptake by caged freshwater mussels suspended within the water column at shoreline sites on the St. Clair and Detroit rivers. They reported detectable total PCB levels in samples primarily from Canadian sites between Windsor and Amherstburg. Kauss and Hamdy (1985) detected QCB, HCB, and OCS in tissues of mussels from sites between Sarnia and Corunna, Ontario. Pugsley et at. (1985) sampled sediments and naturally occurring mussels for OCS throughout the Lake Huron-Lake Erie corridor and found sediments to contain maximal OCS amounts at scattered sites throughout the St. Clair River. Too few mussels were collected from this river for them to ascertain contamination patterns in biota. Despite this overall consistency of results, our ultimate interpretation of the significance of contaminant levels in insects among sites is limited by lack of information regarding larval microhabitats of the animals collected. For example, we cannot be certain that all insects collected at a site emerged locally. Although this is a reasonable assumption for Caenis adults, which are weak fliers and live for only a few hours (Edmunds et at. 1976), caddisfly adults can survive for extended periods and can undertake extensive upstream flights (Roos 1957). Hexagenia adults are susceptible to longdistance transport by prevailing winds . We believe that variation in contaminant concentrations among taxa at single sites partially reflects this differential flight behavior. For example, the marked differences in contaminant levels observed between Hexagenia and Trichoptera collected at the Sarnia site (station 8, Table 3) could be explained in terms of upstream flight tendencies by caddisflies from highly contaminated downstream reaches coincidentally with passive aerial transport of Hexagenia from upwind emergence sites on Lake Huron. Malicky (cited in Chantaramongkol 1983) described a flight range of up to several hundred meters for caddisflies attracted to light traps on large European rivers. Our collection of Macronema zebratum at only the Amherstburg and River Canard sites on the Detroit River is con-
155
sistent with the apparently local distribution of larvae of this species (Thornley and Hamdy 1984) and suggests that Malicky's estimate is generally applicable to the Lake Huron/Lake Erie connecting channel. Dispersal of this magnitude implies that the contaminant concentration measured from an adult insect sample is an integrated value representing biota from a substantial area surrounding the collection site. Observed variation in contaminant level among taxa at a site may additionally reflect differences in microdistribution and/or feeding habits of immatures. Hydropsychid larvae frequent erosional habitats and filter suspended particles from the water using silken nets. Accordingly, the classes of contaminants to which they are exposed during feeding might differ substantially from those of the mayfly taxa that we collected. Both Caenis and Hexagenia inhabit depositional areas. Caenis feed on organic particles that have settled and accumulated on the riverbed. Hexagenia ingest similar food when they leave their burrows to filter at the mud/water interface. Such feeding specializations, especially among Hydropsychidae, could be useful in assessing sources of specific organic contaminants. Some genera, such as Macronema, tend to consume primarily very fine organic particles (Wallace and Sherberger 1974, Wallace 1975) whereas others (e.g., Cheumatopsyche) derive most of their energy from larger particles and small invertebrates (Benke and Wallace 1980). Since many organic contaminants adsorb to small particles « 64 p'm; Eadie et at. 1982a, 1982b), differences in contaminant concentrations among taxa may provide a measure of relative distribution of contaminants among the various food categories. In view of the high contaminant levels that we observed in samples, the ultimate fate of adult insects merits consideration. Most adults undoubtedly die and decompose at their site of mating or oviposition. However, appropriate weather conditions coincident with mass adult emergence can transport large numbers of animals inland. We have no information as to the potential importance of such contaminant transfer to terrestrial habitats relative to other loadings, but believe that it warrants further investigation. Despite the limitations described above, we believe that adult aquatic insects have potential as a cost-effective alternative to sampling organisms directly in the aquatic environment because large numbers can be quickly collected and effectively
156
CIBOROWSKI and CORKUM
used to evaluate local contamination. This eliminates many difficulties associated with aquatic sampling in that little specialized equipment is needed and animals are collected independently of surrounding sediments. ACKNOWLEDGMENTS
International Joint Commission. 1985. Report on Great Lakes water quality 1985. G~at Lakes Water Quality Board. Windsor, Ontario, Canada. Kauss, P. B., and Handy., Y. 1985. Biological monitoring of organochlorine contaminants in the St. Clair and Detroit rivers using introduced clams, Elliptio complanatus. J. Great Lakes Res. 11:247-263. Larsson, P. 1984. Transport of PCBs from aquatic to terrestrial environments by emerging chironomids.
Environ. Pol/ut. 34:283-289.
We wish to thank the Great Lakes Institute (GLI) staff for their assistance in analysing the samples. R. Lazar, B. Muncaster, and S. Noble provided advice on GC preparatory procedures. G. D. Haffner, D. J. Innes, and I. M. Weis reviewed the manuscript. A. V. Provonsha kindly identified Caenis specimens. Costs of sample analysis were defrayed by grants from the Ontario Ministry of the Environment and the World Wildlife Fund to GLI. Other aspects of the project were supported by a grant from the Natural Sciences and Engineering Research Council of Canada to J. J. H. Ciborowski.
Oliver, B. G. 1984. Uptake of chlorinated organics from anthropogenically contaminated sediments by oligochaete worms. Can. J. Fish. Aquat. Sci. 41:878-883. _ _ _ _ , and Bournbonniere, R. A. 1985. Chlorinated contaminants in surficial sediments of Lakes Huron, St. Clair, and Erie: implications regarding sources along the St. Clair and Detroit rivers, J. Great Lakes Res. 11 :366-372. Pugsley, C. W., Hebert, P. D. N., Wood, G. W., Brotea, G., and Obal, T. W. 1985. Distribution of contaminants in clams and sediments from the HuronErie Corridor. I - PCBs and octochlorostyrene. J. Great Lakes Res. 11 :275-289. Roos, T. 1957. Studies on upstream migration in adult stream-dwelling insects. I. Rept. Inst. Freshwat. Res.
REFERENCES
SAS Institute Inc. 1985. SAS user's guide: Statistics. Version 5 edition. Cary, North Carolina: SAS Institute Inc. Smith, V. E., Spurr, J. M., Filkins, J. C., and Jones, J. J. 1985. Organochlorine contaminants of wintering ducks foraging on Detroit River sediments. J. Great
Drottningholm 38:167-193. Ballschmiter, A., and Zell, M. 1980. Analysis of polychlorinated biphenyls (PCB) by glass capillary gas chromatography. Fres. Z. Anal. Chem. 302:20-31. Benke, A. C., and Wallace, J. B. 1980. Trophic basis of production among net-spinning caddisflies in a southern Appalachian stream. Ecology 61:108-118. Chantaramongkol, P. 1983. Light-trapped caddisflies (Trichoptera) as water quality indicators in large rivers: Results from the Danube at Veroce, Hungary.
Aquatic Insects 5:33-37. Dixon, W. J., and Brown, M. B. 1979. BMDP-79. Biomedical Computer Programs, P-series. Berkeley: University of California Press. Eadie, B. J., Faust, W., Gardner, W. S., and Nalepa, T. 1982a. Polycyclic aromatic hydrocarbons in sediments and associated benthos in Lake Erie. Chemos-
phere 11:185-191. _ _ _ _ , Landrum, P. F., and Faust, W. 1982b. Polycyclic aromatic hydrocarbons in sediments, pore water and the amphipod, Pontoporeia hoyi, from Lake Michigan. Chemosphere 11:847-858. Edmunds, G. F., Jr., Jensen, S. L., and Berner, L. 1976. The Mayflies of North and Central America.
Minneapolis: Univ. of Minnesota Press. Frank, R., Holdrinet, M., Braun, H. E., Thomas, R. L., Kemp, A. L. W., and Jaquet, J-M. 1977. Organochlorine insecticides and PCBs in sediments of Lake St. Clair (1970 and 1974) and Lake Erie (1971). Sci. of the Total Environ. 8:205-227.
Lakes Res. 11:231-246. Sokal, R. R., and Rohlf, F. J. 1969. Biometry. San Francisco: W. H. Freeman and Co. Struger, J., Weseloh, D. V., Hallett, D. J., and Mineau, P. 1985. Organochlorine contaminants in herring gull eggs from the Detroit and Niagara rivers and Saginaw Bay (1978-1982): Contaminant discriminants. J. Great Lakes Res. 11 :223-230. Thornley, S., and Hamdy, Y. 1984. An assessment of
the bottom fauna and sediments of the Detroit River. MOE, Southwestern Region and Water Resources Branch Report. February, 1984. Toronto, Ontario. Tuinstra, L. G. M. Th., and Traag, W. A. 1983. Capillary gas chromatographic-mass spectrometric determination of individual chlorobiphenyls in technical Aroclors. J. Assoc. Off. Anal. Chem. 66:708-717. Wallace, J. B. 1975. Food partitioning in net-spinning Trichoptera larvae: Hydropsyche venularis, Cheumatopsyche etrona, and Macronema zebratum (Hydropsychidae). Ann. Entomol. Soc. A mer. 68:463-472. _ _ _ _ , and Sherberger, F. 1974. The larval retreat and feeding net of Macronema transversum Hagen (Trichoptera: Hydropsychidae). Hydrobiologia 45:177-184.
ORGANIC CONTAMINANTS IN ADULT AQUATIC INSECTS OF THE ST. CLAIR AND DETROIT RIVERS, ONTARIO, CANADA
Jan J. H. Ciborowski and Lynda D. Corkum Department of Biological Sciences University of Windsor Windsor, Ontario N9B 3P4 ABSTRACT. Night-flying Trichoptera and Ephemeroptera were attracted using long-wave ultraviolet light and collected from 8 Canadian sites adjacent to the St. Clair and Detroit rivers. Gas chromatographic analysis of the extracts from 40 samples of the insects revealed significant concentrations ofpentachiorobenzene (QCB), hexachlorobenzene (HCB), octachlorostyrene (OCS), and 16 polychlorinated biphenyl (PCB) congeners in almost all animals collected. Principal component analysis accounted for 84 % of variation in contaminant concentration among samples. The principal components (PCs) correlated highly with concentrations of 9 hexa-, hepta-, and octachlorobiphenyls (PC-I,' 46% ofoverall variation), 4 tetra- and pentachlorobiphenyls (PC-II; 17% of variation), QCB, HCB, and OCS (PC-III,' 8%), and 2 trichlorobiphenyls (PCs IV and V; each 6% of variation). Values of PC-I were significantly greater among Detroit River than among St. Clair River samples. Values of PC-II were highest for samples from upstream stations on the two rivers. Values of PC-III were higher for St. Clair River samples than for Detroit River samples. These trends are consistent with patterns observed in other biota and sediment previously collected from equivalent sites. Contaminant levels also varied among taxa collected from the same site, possibly because of different larval feeding habits or microdistribution, or adult flight ability. Collection of adults has potential as an inexpensive alternative to aquatic sampling methods in surveys of biota for organic contamination. ADDITIONAL INDEX WORDS: Toxic substances, chlorinated hydrocarbons, Ephemeroptera, Trichoptera.
INTRODUCTION
effort. Although molluscs can be retrieved and analysed individually, they may occur sporadically and in low densities. Diver-assisted collection alleviates some sampling problems, but poor visibility, strong currents, and hazards associated with commercial shipping traffic render certain habitats inaccessible. Ephemeroptera (mayflies) and Trichoptera (caddisflies) pass most of their lives as aquatic larvae, during which time feeding and benthic movements bring them into intimate contact with suspended and deposited sediments. The winged adults are largely nocturnally active, at which time they disperse, mate, and the females oviposit. Many species are attracted to lights, sometimes in enormous numbers. This is a common summer phenomenon at locations along the St. Clair and Detroit rivers. These rivers have been designated Areas of Concern (International Joint Commission 1985) because of extensive organic contami-
Recent research has increasingly stressed the importance of benthic invertebrates as agents of contaminant transfer between sediments and higher trophic levels in freshwater aquatic systems. Larsson (1984) showed that larval Chironomidae could accumulate significant levels of PCBs from contaminated sediments. Oliver (1984) reported similar capabilities for oligochaete worms. The tendency of bivalve molluscs to selectively accumulate toxic organic compounds has stimulated research to assess their potential utility as biomonitors (Pugsley et al. 1985, Kauss and Hamdy 1985). Investigation of invertebrate contamination in aquatic habitats has been hindered by the difficulties of obtaining samples efficiently, especially in large rivers. Aquatic annelids and larval insects are abundant in both lentic and lotic habitats, but separating organisms from the sediments with which they are collected requires expertise and intensive
148
149
ORGANIC CONTAMINANTS IN AQUATIC INSECTS TABLE1. Location of 1986 sample stations and sunset weather conditions. (DR River, DC = overcast).
= Detroit River, SCR = St.
Clair
Stn.
River
Designation
Latitude (North)
Longitude (West)
Date
(0C)
Sky
Wind (km h- 1)
1 2 3 4 5 6 7 8
DR DR DR DR SCR SCR SCR SCR
Amherstburg R. Canard Windsor A Windsor B Port Lambton Sombra Corunna Sarnia
42°06'01" 42°11'48" 42°18'23" 42°20'27" 42°38'38" 42°45'04" 42°53'26" 42°58'26"
83°06'47" 83°06'13" 83°04'27" 82°56'56" 82°30'14" 82°27'54" 82°27'15" 82°24'32"
5 July 6 July 7 July 9 July 14 July 16 July 15 July 10 July
24 28 24 22 21 22 24 17
high OC hazy high OC clear clear hazy high OC high OC
W 2-5 calm calm calm calm E 2-5 S 2-5 NW 2-5
nant accumulation resulting from release of industrial effluents. The objectives of our study were to determine if adult insects that have emerged from aquatic habitats might be useful as a biomonitoring tool and a cost effective alternative to sampling organisms directly within the aquatic environment. We wished to evaluate whether enough adults, attracted with longwave ultraviolet light, could be collected to permit analysis for organic contaminants, and whether samples from sites on the S1. Clair and Detroit rivers harbored significant contaminant levels. METHODS Sample Collection Adults of aquatic insects were captured at eight Canadian sites approximately 8 km apart along the Detroit and S1. Clair rivers between 4 and 16 July 1986 (Table 1). Stations were selected within 30 m of the east riverbank that provided a clear view of the river. Sampling was conducted on warm, relatively calm evenings from near sunset (2130 h EDT) until approximately 2300 h EDT (Table 1). A white cotton sheet, which served as a light reflector and as a substrate for insects, was placed over an automobile hood. Adults were attracted using a 12V115W DC fluorescent long-wave ultraviolet (UV) lamp (length, 45 cm) placed on the sheet and powered from the automobile battery. Mode of collection varied with taxa. Adult Trichoptera were captured using hexane-rinsed 500-mL amber glass jars. Jar lids had a hole cut into their center to accommodate the narrow end of a 12.S-cm dia. funnel. Insects were guided onto the inner surface of the funnel and tapped into the
Temp.
jar. Several g of dry ice within the jar both anaesthetized and cooled trapped insects. Hexagenia (Ephemeroptera) adults that alighted on the sheet were grasped by the wings and placed in amber jars containing dry ice. Upon completion of sampling, the sheet was quickly folded to retain insects that had not been individually captured and transported to the laboratory in a cooler containing dry ice. All organisms were stored overnight in a freezer at -20°C prior to processing. Sample Processing The small size of the insects necessitated pooling organisms prior to analysis. The number of animals comprising a sample depended upon both individual size and quantities collected. In the laboratory, animals were sorted into precleaned glass containers using hexane-rinsed forceps. Although many taxa were attracted to the UV light and incidentally captured, only four were sufficiently widespread and abundant to be used for contaminant analysis. We retained mayflies (Hexagenia and Caenis) and caddisflies (Macronema and "others"). "Other" caddisflies consisted of animals of size and coloration predominant at a particular site; unusual specimens were not included. Trichoptera were sorted without the aid of magnification by summer assistants having minimal entomological training. Preliminary weighing of individuals of each taxon at each site was conducted to estimate numbers adequate for a sample. We attempted to divide animals evenly to produce at least two replicates, each of a total fresh weight between 2 and 6 g. A subsample of organisms was taken from each replicate for further taxonomic analysis (including up to 100 "other" caddisflies per site, as
150
CIBOROWSKI and CORKUM
available) and biomass determination. Samples for contaminant analysis were stored at -20°C for up to 6 weeks prior to extraction. Animals used for biomass determination were weighed singly (Macronema, Hexagenia) or in groups of 6 (other Trichoptera) or 25 (Caenis) to the nearest 0.1 mg on a Sartorius model 2462 balance immediately after sorting, and again after drying at 60°C for 24 h. Sample biomasses were estimated by multiplying the number of animals in a sample by the mean dry weight of animals in the corresponding biomass subsample. Extraction and Contaminant Analysis Analysis for contaminants was performed by the Great Lakes Institute analytical laboratory, University of Windsor, following methods outlined by Pugsley et af. (1985). Samples were placed in 120 mL of acetonitrile with 40 mL water and homogenized for 1-1.5 min with a polytron blender. The fluid was filtered under vacuum through a sintered glass funnel and placed in a separatory funnel. The homogenization/filtration procedure was repeated once using 50 mL of fresh acetonitrile, and twice more with 20-mL lots of acetonitrile. One mL of concentrated sulphuric acid was added to hydrolyze lipids. The filtrate was then extracted by shaking for 2 min with a 150 mL portion and then two 75 mL portions of petroleum ether. The petroleum ether extract was washed with 200 mL of water and then dried by passage through a column containing 15 g of anhydrous sodium sulphate. Samples were cleaned up by passage through 20 mm x 40 cm glass columns containing 1-2 cm of anhydrous sodium sulphate over 20 g of Florisil, eluted with 200 mL of petroleum ether, and then concentrated to 5 mL with a Kuderna-Danish evaporator. Contaminant extracts were analyzed by injection of 1-p.L samples into a Hewlett-Packard model 5790A gas chromatograph (GC) equipped with a 25 m x 0.25 mm fused silica column (J & W Scientific) and an electron capture detector. Splitless injection mode was used at an injector temperature of 250°C. The column was temperature programmed for 0.5 min at 50°C, heated to 250°C at 2°C min- 1 and held for 20 min at 250°C. Detector temperature was 300°C. Helium carrier gas was delivered at a rate of 1.5 mL min-I. Detector makeup gas consisted of 5070 methane-95% argon at 35 mL min-I. Peak areas of contaminants and standards were measured with a Hewlett-Packard
model 3390A integrator. A blank analysis was conducted with each analytic series (2-5 randomly selected samples). Contaminants were quantified against a standard mixture consisting of octachlorostyrene (OCS), pentachlorobenzene (QCB), and hexachlorobenzene (HCB), each at 5.0 p.g kg-I, and Aroclors 1242, 1254, and 1260, each at 20 p.g kg-I. Identification and quantification of 16 PCB congeneric constituents (see Table 3) was based on peak patterns, relative retention times, and relative composition of Aroclors as presented by Tuinstra and Traag (1983). Because relative composition of congeners in Aroclors can vary from lot to lot, concentrations of PCBs presented are tentative and must be regarded as relative rather than absolute; however, the data are admissible for comparative purposes among samples. Analysis of blind samples for total PCBs produces results within 5% of true values (1986 International Joint Commission Quality Assurance Program). Equipment failures necessitated refrigerating some extracted samples for up to 18 d prior to GC analysis. This introduced substantial variation to replicates (stored samples had higher apparent concentrations of contaminants due to solvent evaporation). To evaluate this, relative concentration of each sample (Y/Y, where Y is the mean of all replicates of one taxon at one station) was regressed against storage time for each of the contaminants examined. Significant relationships (p < 0.01) between relative concentration and storage time were found for 11 of 19 compounds (maximum R2 = 0.39, overall median R2 = 0.22). Accordingly, values of each contaminant were statistically adjusted to a standard storage time according to the derived regression equations (Sokal and Rohlf 1969, pp. 444-445). This procedure reduces the variance among replicates taken as a group, without affecting the mean value of these replicates. Insufficient material was available to permit assessment of recovery efficiency or insect lipid content. Recovery efficiencies for our system using bivalve tissues average 70-85% for HCB, OCS, QCB, and total PCBs (Pugsley et af. 1985; unpublished data). Calculations were not corrected for procedural losses. Statistical Analyses Concentrations of many of the compounds were highly correlated with one another among repli-
151
ORGANIC CONTAMINANTS IN AQUATIC INSECTS cates, taxa, and sites. Consequently, principal component analysis (PCA; Dixon and Brown 1979) was used to reduce the data set prior to further statistical analysis. Concentrations were Ln(Y + 1) transformed prior to analysis. Following the PCA analysis, we determined the degree of association between the original 19 variables (compounds) and the derived principal components using Spearman's rank correlation coefficient (Sokal and Rohlf 1969). Analyses of variance (ANOVA, unbalanced hierarchical design; SAS Institute Inc. 1985) were then used to test for differences in values of the principal components among rivers and sites for each taxon, and also pairs of taxa occurring at common sites. Significant differences detected among principal components scores imply equivalent differences in the concentrations of the contaminants associated with each component. RESULTS A total of 40 samples was analyzed for PCBs and three other organochlorine compounds, of which one sample was strongly deviant from replicates and was discarded. Adults of Trichoptera were the only organisms collected at all stations. The caddisfly Macronema zebratum Hagen (Hydropsychidae), whose larvae are filter-feeders, comprised the entire Trichoptera collection at Amherstburg. Samples of Trichoptera from other stations were also dominated by genera of hydropsychid net-spinning caddisflies; primarily Cheumatopsyche spp (Table 2). Leptoceridae were the only other caddisflies commonly collected. They dominated samples at Port Lambton. Mayflies, Caenis (primarily C. latipennis Banks) and Hexagenia (mostly H. limbata (Serville», were each collected at four stations. Overall abundance of flying adults was much reduced at the three upstream sites of the St. Clair River. This was reflected in the reduced number of replicates analyzed from these areas. All taxa at all sites contained detectable levels of both PCBs and other organochlorine compounds (Table 3). Five principal components accounted for 84070 of the variation in contaminant concentrations among samples. The first principal component (PC-I) accounted for 46% of overall variation and was highly positively correlated with concentrations of nine PCB congeners (primarily hexa-, hepta-, and octachlorobiphenyls) and negatively correlated with HCB concentration (Table 4). PC-II explained an additional 17070 of variation
TABLE 2. Relative taxonomic composition (percent) of "other" Trichoptera used in contaminant analysis. Figures in bold face are family totals. All specimens collected at station 1 were Macronema zebratum (Hydropsychidae). Taxon
1
2
3
STATION 4 5 6
Hydropsychidae 100 70 84 94 Cheumatopsyche spp 64 76 94 Hydropsyche spp 6 7 1 Potamyia sp. 0 0 0 Lepidostomatidae Lepidostoma sp. 30 16 6 Leptoceridae Ceraclea spp - 21 16 4 Mystacides spp Oecetus spp 8 1 - Triaenodes sp. Unidentified 1 0 0 0 Molannidae Molanna sp. 0 0 0 Polycentropodidae Neureclipsis sp. Polycentropus sp. - - NA 100 100 103 Total No. examined
7
8
36 65 98 98 27 52 82 94 9 13 16 4 0 13 13 59 22 16 13 4 30 9 9 1 0 0
-
5 I
0
-
0
-
0 -
2
1 1
-
2 0 0
1 1 0
-
4 70 23 99 100
and was associated with five tetra- and pentachlorobiphenyls. Three contaminants, QCB, HCB, and OCS, were positively correlated with values of PC-III, which accounted for 8% of overall variation. PC-IV and PC-V were each highly correlated with a different trichlorobiphenyl and each removed an additional 6% of variation. Spatial trends in contaminant concentrations were evident for all taxa, and these patterns are reflected in site-to-site variation in mean principal component scores (Fig. 1). Detroit River samples of Trichoptera (stations 1-4, Table 3) had high concentrations of highly chlorinated PCBs (PCBs associated with PC-I) and relatively low non-PCB organochlorine concentrations. Maximum concentrations of each of the PCB congeners (except PCB 18) were recorded in Trichoptera from the two Windsor stations (stations 3 and 4, Table 3). Mean values of PC-I for Detroit River Trichoptera were significantly greater than values for the St. Clair River (Fig. lA; p < 0.01). In contrast, Trichoptera collected from the St. Clair River (stations 5-8, Table 3) had significantly higher QCB, OCS, and especially HCB concentrations than their Detroit River counterparts. This was reflected in significant differences in mean scores of PC-III (Fig. lC; P < 0.01). Significant variation was also evident among trichopteran samples collected from upstream versus
10-0 CIt
N
TABLE 3.
Mean (and S.E.) concentration of organic contaminants (p.g kg-I dry weight) in aquatic insect taxa among stations. CONTAMINANT
Stn.
Taxon
1 Macronema
No. -1 Dry sample WI. (g) N 150 1.9328
5
QCB
HCB
OCS
PCB 18
3.99 (1.497)
32.94 (2.811)
42.98 (3.601)
0.06 (0.057)
10.75 NA
21.18 NA
PCB 28
PCB 52
PCB 66
PCB 87
PCB 95
PCB 97
PCB 101
PCB 118
PCB 138
PCB 141
PCB 153
PCB 170
PCB 180
PCB 187
PCB 194
1.98 (0.435)
3.75 (0.471)
20.4 (2.472)
2.84 (0.399)
7.77 (1.581)
1.86 (0.204)
19.02 (5.853)
13.80 (3.066)
25.71 (2.991)
2.97 (1.401)
29.25 (3.732)
6.30 (3.366)
22.80 (3.360)
12.33 (1.242)
3.78 (1.152)
1.50 NA
1.92 NA
10.44 NA
15.78 NA
27.33 NA
2.25 NA
35.52 NA
22.62 NA
34.02 NA
17.49 NA
12.81 NA
8.55 NA
Macronema
108
Trichoptera (Other)
500 0.8958 3
1.28 (0.648)
19.51 (1.844)
36.21 (4.647)
0.63 (0.543)
2.01 (0.660)
9.60 (2.772)
19.17 (4.503)
6.30 (1.767)
23.88 (6.600)
4.05 (0.873)
25.74 (6.882)
30.48 (7.833)
45.06 (12.138)
9.96 (3.564)
48.84 (12.882)
11.40 (6.108)
37.41 (12.144)
20.13 (5.493)
4.11 (1.212)
1.2536 2
2.24 (0.310)
25.54 (4.776)
10.47 (0.185)
0.57 (0.750)
1.83 (0.510)
8.58 (2.466)
15.30 (2.124)
5.10 (1.017)
13.56 (1.587)
4.29 (0.933)
14.37 (4.554)
13.65 (4.257)
19.62 (3.543)
1.35 (1.347)
20.64 (4.758)
1.35 (0.078)
9.27 (3.084)
5.52 (1.362)
0.84 (0.846)
3
1.50 (0.274)
15.65 (2.376)
35.79 (3.992)
0.87 (0.471)
2.67 (1.581)
12.75 (3.888)
23.64 (3.717)
8.79 (1.377)
29.22 (1.575)
5.07 (0.831)
38.22 (4.935)
46.32 (10.095)
62.25 (11.694)
19.59 (4.146)
76.56 (15.462)
24.24 (7.143)
70.02 (15.549)
36.27 (6.798)
12.12 (1.632)
2000 0.7200 2
1.16 (1.162)
21.88 (1.705)
17.54 (0.126)
0.72 (0.708)
6.18 (0.279)
8.16 (8.151)
32.82 (1.377)
10.08 (0.384)
32.70 (1.611)
6.63 (0.330)
28.89 (0.627)
23.91 (0.174)
42.33 (2.193)
9.78 (1.086)
37.59 (0.027)
6.87 (6.858)
19.26 (0.228)
17.67 (3.900)
2.13 (0.219)
Caenis Trichoptera (Other)
Caenis
1850 550
1.1718
1.1568
l'
<0.49 NA
<0.09 NA
2.28 NA
<3.84 NA
1.56 NA
..=
n 0
:=
600
1.1111
4
2.65 (0.382)
20.77 (1.588)
40.94 (9.069)
0.84 (0.195)
2.01 (0.726)
11.88 (1.797)
22.44 (3.027)
10.38 (1.608)
24.84 (0.480)
6.39 (1.077)
30.48 (4.188)
35.04 (17.619)
62.64 (6.933)
11.01 (1.950)
59.34 (16.050)
14.28 (5.736)
55.14 (11.271)
24.45 (5.352)
4.95 (1.347)
~
Hexagenia
110
1.2578
3
9.48 119.25 (0.750) (7.746)
17.33 (1.469)
0.09 (0.092)
0.27 (0.261)
4.92 (0.738)
10.23 (1.554)
2.94 (0.504)
11.49 (0.927)
3.21 (0.432)
8.34 (2.313)
9.09 (2.034)
16.65 (0.600)
3.03 (1.065)
18.45 (2.835)
3.09 (1.590)
10.53 (2.361)
5.34 (0.756)
2.16 (1.140)
~
Trichoptera (Other)
375 0.9222
2
2.84 (1.134)
0.36
6.95 (3.498)
8.10 (0.945)
4.68 (1.230)
4.17 (1.266)
2.34 (1.095)
18.18 (14.580)
11.91 (3.480)
20.88 (4.578)
1.68 (0.078)
18.39 (4.962)
4.17 (4.179)
12.51 (4.080)
4.74 (0.027)
4 Trichoptera (Other)
Caenis Hexagenia 6 Trichoptera (Other)
Caenis Hexagenia Trichoptera
3750
1.2747 3
120 2.0274 2
Hexagenia
16.Q7 222.68 253.32 (1.077) (24.677) (17.454)
0.30 (0.366)
0.06 (0.042)
2.55 (2.541)
19.29 (2.709)
27.30 5.76 (2.886) (14.061)
4.68 (0.351)
17.28 (1.656)
15.03 (2.010)
20.13 (1.584)
1.14 (0.288)
16.98 (1.644)
0.12 (0.108)
6.27 (1.242)
3.72 (0.804)
0.36 (0.219)
n
1.50 (0.211)
0.18 (0.009)
0.36 (0.001)
4.14 (1.836)
9.21 (1.569)
1.92 (0.024)
8.49 (3.357)
1.41 (0.027)
5.40 (0.273)
4.35 (0.336)
6.00 (0.495)
0.57 (0.084)
8.01 (0.723)
3.63 (1.701)
4.35 (0.900)
1.68 (0.420)
0.93 (0.051)
~~
31.35 (7.229)
6.10 (1.514)
1
3.73 NA
45.28 NA
261.19 NA
2.73 NA
<0.15 NA
7.56 NA
14.64 NA
6.69 NA
8.28 NA
3.57 NA
17.79 NA
7.05 NA
27.06 NA
2.34 NA
18.60 NA
<0.33 NA
36.60 NA
4.44 NA
5.85 NA
1000
1.0650
1
6.23 NA
84.95 NA
97.98 NA
0.15 NA
0.06 NA
8.19 NA
13.05 NA
4.32 NA
23.88 NA
2.97 NA
11.61 NA
9.30 NA
11.31 NA
0.60 NA
9.93 NA
<0.15 NA
2.94 NA
2.16 NA
0.63 NA
82
1.3962
I
3.70 NA
133.30 NA
36.22 NA
0.48 NA
0.90 NA
3.30 NA
10.65 NA
3.48 NA
8.46 NA
2.58 NA
15.33 NA
10.05 NA
16.20 NA
1.68 NA
19.17 NA
7.23 NA
9.51 NA
3.96 NA
<0.21 NA
3.48 (3.474)
13.05 (1.221)
5.31 (1.794)
<0.24 NA
4.89 (1.221)
2.49 (2.496)
0.54 (0.318)
15.78 (0.579)
6.24 (1.080)
5.49 (0.180)
500
1.2450 2
2.06 (0.105)
40.42 181.07 (0.004) (31.434)
0.69 (0.267)
0.72 (0.306)
3.69 (0.348)
14.64 (4.092)
5.46 (0.777)
13.20 (6.255)
3.18 (0.387)
14.25 (1.659)
9.36 (1.338)
25.98 (3.300)
2.61 (1.113)
18.27 (2.052)
325
1.2144 2
21.37 187.27 415.40 (3.072) (27.591) (100.029)
0.54 (0.726)
0.66 (0.660)
16.05 (10.698)
20.43 (4.965)
33.27 9.81 (4.959) (23.688)
6.12 (2.175)
28.80 (13.380)
18.42 (8.514)
16.95 (0.174)
1.35 (1.338)
14.79 (0.603)
67
0.8546 2
2.62 (2.617)
8.46 (0.619)
8.76 (2.218)
6.24 (0.795)
15.03 (7.425)
6.33 (1.920)
23.49 (1.920)
14.94 (0.741)
21.03 (1.692)
4.89 (0.987)
37.53 (2.238)
• 1 replicate discarded.
~
~0.351)
0.63 (0.630)
0.4783
(Other)
00
48.48 147.19 (8.140) (39.937)
175
(Other) Trichoptera
<0.30 NA
..
18.63 <0.41 (2.049) NA
<0.15NA
<0.09 NA
<0.12 NA 5.85 (4.347)
=-=
0
ORGANIC CONTAMINANTS IN AQUATIC INSECTS TABLE 4.
153
Correlation between concentration 0/ organic contaminants and principal components.
Principal Component Compound Designation 1 PC-I PC-II PC-III PC-IV PC-V 2,2',3,4,4',5,5'-Heptachlorobiphenyl PCB 180 -0.191 0.183 0.216 0.889** 0.151 2,2',4,4',5,5'-Hexachlorobiphenyl PCB 153 -0.171 0.233 0.879** 0.328 0.024 2,2',3,4',5,5',6'-Heptachlorobiphenyl PCB 187 -0.214 0.364 0.004 0.842** 0.195 2,2',3,4,4',5'-Hexachlorobiphenyl PCB 138 -0.063 0.319 0.225 0.824** 0.318 2,2',3,3',4,4',5,5'-Octachlorobiphenyl PCB 194 -0.200 -0.061 -0.133 0.824** 0.226 2,2', 3,4,5,5'-Hexachlorobiphenyl PCB 141 0.043 -0.128 0.026 0.805** 0.400 2,3',4,4',5-Pentachlorobiphenyl PCB 118 0.084 0.147 0.093 0.756** 0.457* 2,2',4,5,5'-Pentachlorobiphenyl PCB 101 0.082 0.644** 0.523** 0.086 0.297 2,2',3,3',4,4',5-Heptachlorobiphenyl PCB 170 -0.380 0.073 0.532** 0.124 0.273 2,3',4,4'-Tetrachlorobiphenyl PCB 66 0.430* 0.242 0.454* 0.498* 0.111 2,2' ,3' ,4,5-Pentachlorobiphenyl PCB 97 0.866** 0.048 0.061 0.262 0.144 2,2',3,5',6-Pentachlorobiphenyl PCB 95 0.825** 0.073 0.198 0.163 -0.124 2,2',5,5'-Tetrachlorobiphenyl PCB 52 0.783** -0.114 -0.211 0.155 0.061 2,2',3,4,5'-Pentachlorobiphenyl PCB 87 0.376 0.739** 0.053 0.120 0.448* Pentachlorobenzene QCB 0.091 0.819** -0.135 -0.227 -0.206 Hexachlorobenzene HCB 0.787** -0.217 -0.019 -0.458* -0.239 OCS Octachlorostyrene 0.759** -0.017 -0.108 0.329 0.026 2,4,4'-Trichlorobiphenyl PCB 28 0.018 -0.281 0.900** 0.084 0.247 2,2',5-Trichlorobiphenyl PCB 18 0.269 0.159 0.045 0.847** 0.107 IPCB numbering follows Ballschmiter and Zell 1980. *p
downstream sites within each river. Samples from upstream stations had higher concentrations of 4-, 5-, and 6-chlorine PCBs (those associated with PCII) than occurred in downstream samples (PCBs 52 to 153, Table 3). However, whereas the contrasts for samples from the Detroit River occurred between the two upstream stations (3 and 4) and the two downstream sites (1 and 2), St. Clair River station differences were between the single Sarnia site (8) and the three downstream stations (5, 6, and 7, Table 3). Analysis of variance indicated significant within-river differences among PC-II scores, with which these PCB congeners were highly correlated (Fig. IB; P < 0.05). Values of PC-II did not differ between rivers (p > 0.05). There were no discernable trends in concentration of the two trichlorobiphenyls found in Trichoptera (p > 0.05; Figs. ID and IE). Ephemeroptera tended to have low concentrations of PCBs associated with PC-I relative to Trichoptera from comparable sites (stations 4, 5, 7, and 8, Table 3; Fig. IA). Hexagenia samples from Sarnia (station 8) had higher concentrations of PCBs associated with PC-II (Fig. IB) and lower non-PCB organochlorine concentrations (Fig. IC) than did Hexagenia samples from stations upstream and downstream of Lake St. Clair (sta-
tions 4, 5, and 6). Overall, Trichoptera had significantly higher levels of QCB, HCB, and OCS than did Hexagenia (expressed as mean PC-III values, Fig. IC; p < 0.05). Samples of Caenis varied among sites primarily with reference to QCB, HCB, and OCS concentrations (Table 3). Samples from the St. Clair River (stations 5 and 6) had much higher concentrations of these chemicals than did collections from the Detroit River (stations 2 and 3, Table 3). St. Clair River Caenis in general also had greater concentrations of the three non-PCB compounds than did either Trichoptera or Hexagenia occurring at equivalent sites (p < 0.05; Fig. IC). Caenis samples from the upper Detroit River (station 3) differed from remaining Caenis samples (stations 2, 5, and 6) in having greater levels of highly chlorinated PCBs (associated with PC-I, Fig. IA) and lower concentrations of HCB (Table 3). DISCUSSION To be potentially useful for biomonitoring, naturally occurring organisms should meet several criteria. Taxa should be widespread and accessible across a range of environmental conditions. Samples must provide data sufficiently precise that site-
154
cmOROWSKI and CORKUM 2
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0 -1
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A
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1
-2
I
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a..
I
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234 Detroit R.
5
678 St. Clair R.
Station FIG. 1. Means (± 1 S.E.) of principal component scores for insect samples collected at various sites on the Detroit and St. Clair rivers. Station numbers correspond to those listed in Table 1. Solid lines and circles, all Trichoptera; dashed lines and open circles, Caenis; open squares, Hexagenia. A: PC-I, correlated with concentrations of PCBs 101, 118, 138, 141, 153, 170, 180, 182, and 194; B: PC-II, correlated with PCBs 52, 66, 87, 95, 97, and 101; C: PC-III, correlated with QCB, HCB, and OCS; D: PC-IV, correlated with PCB 28 and PCB 66; E: PC- V, correlated with PCB 18 and PCB 87.
to-site variation can be discerned with reasonable confidence; and the derived measurements must accurately reflect contaminant patterns of the biota at large. Our study shows that adult aquatic
insects may be easily collected using UV light attraction in numbers adequate for contaminant analysis. Variability in contaminant concentrations was sufficiently low that we could detect significant differences in contaminants among taxa and within single taxa among sites. Note, however, that our "replicates" at sites represent single, large samples that were partitioned in the laboratory. Accordingly, they reflect variation in our subsampling and processing methods rather than on-site environmental variability. Nevertheless, each collection represents an integrated sample of individuals from a potentially extensive surrounding area. Spatial patterns of contamination indicated by our samples appear to correspond with results of other studies of organic contaminants in biota and sediments of the St. Clair and Detroit rivers. Trichoptera were present at all eight sites of both the Detroit and St. Clair rivers; Caenis were collected at two sites on each river; and three of four Hexagenia sites were located on the St. Clair River. Concentrations of highly chlorinated PCBs (hexa-, hepta-, and octachlorobiphenyls) were significantly greater in Trichoptera emerging from Detroit River sites than in samples from St. Clair River sites. Levels of non-PCB organochlorine compounds (QCB, HCB, and OCS) were higher in Trichoptera collected from the St. Clair River than from the Detroit River. Additionally, upstream/ downstream variation in contaminant concentrations was evident in both rivers; greatest concentrations of less highly chlorinated PCBs (tri-,tetra-, and pentachlorobiphenyls) were found in samples from upstream sites. Similar spatial trends were evident among sites for the mayfly, Caenis. Yet concentrations of both PCBs and certain other organochlorides in Caenis differed from levels in the caddisflies. Concentrations of HCB were typically higher in the mayfly taxa than in caddisflies, with the exception of the Sarnia samples, where the trend was reversed. Our detection of elevated OCS concentrations at St. Clair River sites and high PCB levels at upstream Detroit River sites is consistent with assessments of local contamination by earlier workers (e.g., Thornley and Hamdy 1984, Kauss and Hamdy 1985, Pugsley et af. 1985, Struger et af. 1985). Several studies (Frank et af. 1977, Thornley and Hamdy 1984, Kauss and Hamdy 1985, Oliver and Bournbonniere 1985, Smith et af. 1985) cite the Detroit River's western (USA) shore as the major source of PCBs deposited in the western basin of
ORGANIC CONTAMINANTS IN AQUATIC INSECTS
Lake Erie. Thornley and Hamdy (1984) reported sediment total PCB concentrations in excess of Ontario guidelines (50 p.g/kg) for dredging at over 59010 of Detroit River sites that they sampled. Among the Canadian samples they examined, greatest total PCB concentrations occurred within an area that includes our two upstream sites on the Detroit River. Kauss and Hamdy (1985) examined short-term contaminant uptake by caged freshwater mussels suspended within the water column at shoreline sites on the St. Clair and Detroit rivers. They reported detectable total PCB levels in samples primarily from Canadian sites between Windsor and Amherstburg. Kauss and Hamdy (1985) detected QCB, HCB, and OCS in tissues of mussels from sites between Sarnia and Corunna, Ontario. Pugsley et at. (1985) sampled sediments and naturally occurring mussels for OCS throughout the Lake Huron-Lake Erie corridor and found sediments to contain maximal OCS amounts at scattered sites throughout the St. Clair River. Too few mussels were collected from this river for them to ascertain contamination patterns in biota. Despite this overall consistency of results, our ultimate interpretation of the significance of contaminant levels in insects among sites is limited by lack of information regarding larval microhabitats of the animals collected. For example, we cannot be certain that all insects collected at a site emerged locally. Although this is a reasonable assumption for Caenis adults, which are weak fliers and live for only a few hours (Edmunds et at. 1976), caddisfly adults can survive for extended periods and can undertake extensive upstream flights (Roos 1957). Hexagenia adults are susceptible to longdistance transport by prevailing winds . We believe that variation in contaminant concentrations among taxa at single sites partially reflects this differential flight behavior. For example, the marked differences in contaminant levels observed between Hexagenia and Trichoptera collected at the Sarnia site (station 8, Table 3) could be explained in terms of upstream flight tendencies by caddisflies from highly contaminated downstream reaches coincidentally with passive aerial transport of Hexagenia from upwind emergence sites on Lake Huron. Malicky (cited in Chantaramongkol 1983) described a flight range of up to several hundred meters for caddisflies attracted to light traps on large European rivers. Our collection of Macronema zebratum at only the Amherstburg and River Canard sites on the Detroit River is con-
155
sistent with the apparently local distribution of larvae of this species (Thornley and Hamdy 1984) and suggests that Malicky's estimate is generally applicable to the Lake Huron/Lake Erie connecting channel. Dispersal of this magnitude implies that the contaminant concentration measured from an adult insect sample is an integrated value representing biota from a substantial area surrounding the collection site. Observed variation in contaminant level among taxa at a site may additionally reflect differences in microdistribution and/or feeding habits of immatures. Hydropsychid larvae frequent erosional habitats and filter suspended particles from the water using silken nets. Accordingly, the classes of contaminants to which they are exposed during feeding might differ substantially from those of the mayfly taxa that we collected. Both Caenis and Hexagenia inhabit depositional areas. Caenis feed on organic particles that have settled and accumulated on the riverbed. Hexagenia ingest similar food when they leave their burrows to filter at the mud/water interface. Such feeding specializations, especially among Hydropsychidae, could be useful in assessing sources of specific organic contaminants. Some genera, such as Macronema, tend to consume primarily very fine organic particles (Wallace and Sherberger 1974, Wallace 1975) whereas others (e.g., Cheumatopsyche) derive most of their energy from larger particles and small invertebrates (Benke and Wallace 1980). Since many organic contaminants adsorb to small particles « 64 p'm; Eadie et at. 1982a, 1982b), differences in contaminant concentrations among taxa may provide a measure of relative distribution of contaminants among the various food categories. In view of the high contaminant levels that we observed in samples, the ultimate fate of adult insects merits consideration. Most adults undoubtedly die and decompose at their site of mating or oviposition. However, appropriate weather conditions coincident with mass adult emergence can transport large numbers of animals inland. We have no information as to the potential importance of such contaminant transfer to terrestrial habitats relative to other loadings, but believe that it warrants further investigation. Despite the limitations described above, we believe that adult aquatic insects have potential as a cost-effective alternative to sampling organisms directly in the aquatic environment because large numbers can be quickly collected and effectively
156
CIBOROWSKI and CORKUM
used to evaluate local contamination. This eliminates many difficulties associated with aquatic sampling in that little specialized equipment is needed and animals are collected independently of surrounding sediments. ACKNOWLEDGMENTS
International Joint Commission. 1985. Report on Great Lakes water quality 1985. G~at Lakes Water Quality Board. Windsor, Ontario, Canada. Kauss, P. B., and Handy., Y. 1985. Biological monitoring of organochlorine contaminants in the St. Clair and Detroit rivers using introduced clams, Elliptio complanatus. J. Great Lakes Res. 11:247-263. Larsson, P. 1984. Transport of PCBs from aquatic to terrestrial environments by emerging chironomids.
Environ. Pol/ut. 34:283-289.
We wish to thank the Great Lakes Institute (GLI) staff for their assistance in analysing the samples. R. Lazar, B. Muncaster, and S. Noble provided advice on GC preparatory procedures. G. D. Haffner, D. J. Innes, and I. M. Weis reviewed the manuscript. A. V. Provonsha kindly identified Caenis specimens. Costs of sample analysis were defrayed by grants from the Ontario Ministry of the Environment and the World Wildlife Fund to GLI. Other aspects of the project were supported by a grant from the Natural Sciences and Engineering Research Council of Canada to J. J. H. Ciborowski.
Oliver, B. G. 1984. Uptake of chlorinated organics from anthropogenically contaminated sediments by oligochaete worms. Can. J. Fish. Aquat. Sci. 41:878-883. _ _ _ _ , and Bournbonniere, R. A. 1985. Chlorinated contaminants in surficial sediments of Lakes Huron, St. Clair, and Erie: implications regarding sources along the St. Clair and Detroit rivers, J. Great Lakes Res. 11 :366-372. Pugsley, C. W., Hebert, P. D. N., Wood, G. W., Brotea, G., and Obal, T. W. 1985. Distribution of contaminants in clams and sediments from the HuronErie Corridor. I - PCBs and octochlorostyrene. J. Great Lakes Res. 11 :275-289. Roos, T. 1957. Studies on upstream migration in adult stream-dwelling insects. I. Rept. Inst. Freshwat. Res.
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SAS Institute Inc. 1985. SAS user's guide: Statistics. Version 5 edition. Cary, North Carolina: SAS Institute Inc. Smith, V. E., Spurr, J. M., Filkins, J. C., and Jones, J. J. 1985. Organochlorine contaminants of wintering ducks foraging on Detroit River sediments. J. Great
Drottningholm 38:167-193. Ballschmiter, A., and Zell, M. 1980. Analysis of polychlorinated biphenyls (PCB) by glass capillary gas chromatography. Fres. Z. Anal. Chem. 302:20-31. Benke, A. C., and Wallace, J. B. 1980. Trophic basis of production among net-spinning caddisflies in a southern Appalachian stream. Ecology 61:108-118. Chantaramongkol, P. 1983. Light-trapped caddisflies (Trichoptera) as water quality indicators in large rivers: Results from the Danube at Veroce, Hungary.
Aquatic Insects 5:33-37. Dixon, W. J., and Brown, M. B. 1979. BMDP-79. Biomedical Computer Programs, P-series. Berkeley: University of California Press. Eadie, B. J., Faust, W., Gardner, W. S., and Nalepa, T. 1982a. Polycyclic aromatic hydrocarbons in sediments and associated benthos in Lake Erie. Chemos-
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