NOTES
Cadmium, Nickel, Lead, and Zinc in Earthworms from Roadside Soil Charles D. Gish’ and Robert
E. Christensen2
Patuxent Wildlife R e s e a r c h Center, B u r e a u of Sport Fisheries a n d Wildlife, Laurel, M d . 20810
Cd, Ni, P b , and Zn in soils a n d earthworms along two Maryland highways decreased with increasing distance (10, 20, 40, 80, and 160 f t ) from t h e roadway. Metals were quantified by atomic absorption spectrophotometry. Metal residues were higher a t the location along each highway where traffic volume was greater. Correlations between residues in earthworms and soil decreased with decreasing atomic weights ( P b > Cd > Zn > Ni). Metal residues in soils were positively correlated with quantities of soil organic matter. Earthworms accumulated u p to 331.4 ppm of P b and 670.0 of Zn, concentrations which may be lethal to earthworm-eating animals. Lead ( P b ) accumulations have been found in soil and vegetation along heavily traveled highways; levels of accumulation were positively related to traffic volume and negatively related to distance from highway (Lagerwerff and Specht, 1970; Motto et al., 1970; Page and Ganje, 1970; Chow, 1970). Lagerwerff and Specht (1970) also reported elevated levels of cadmium (Cd), nickel (Nij, and zinc ( Z n ) in both soils and vegetation; they attributed P b and Ni to gasoline. and Cd and Zn both to tires and motor oil. Earthworms and other soil animals accumulate organochlorine insecticides in concentrations generally greater than those in the soils [see Gish (1970) and Korschgen (1970) for additional references], but little attention has been given to metals in soil organisms. We compared residues of heavy metals in earthworms and soils with distance from roadway and traffic volume. Experimental Worms and soils were collected in 1970 (Table I) a t two locations along the Baltimore-Washington Parkway, 12.7 mi south of Maryland Highway 197 (location A) and 42 mi south of Maryland 175 (B). a n d a t two locations along L.S. Highway 1. 1.3 and 3.7 mi south of Maryland 197 (C and D ) . Soils sampled along the Baltimore-Washington Parkway could not be classified (Table I ) since land operations had destroyed soil profiles. Location A sloped downward at about 15”, and location B upward at about 15’. U.S. Highway 1 locations were essentially level with the roadway. “Control” samples were taken a t five locations on the Patuxent Wildlife Research Center from level fields isolated from traffic by distance and by stands of trees. Soils and earthworms were collected from five plots a t each of the four highway locations; plots were 10, 20, 40, 80, and 160 ft from the edge of the pavement. Only the top inch of soil was kept for analysis. Soils were frozen in jars cleaned by immersing in 10% nitric acid for one hour, then rinsing in deionized water. Earthworms. obtained by
Present address. Division of Wildlife Refuges, U.S.Department of the Interior. Washington. D.C. 20240. To whom correspondence should be addressed. Present address, IVAIIF Institute, Inc., Box 2,599. Madishn, Wis. 53701. 1060
Environmental Science 8 Technology
hand-sorting the soil, included immature and adult stages of Lumbricus terrestris, Allolobophora chlorotica, A . trapezoides, A . turgida, and some unidentifiable juveniles. A. trapetoides and A. turgida were most abundant. All worms from a single plot were pooled into one jar and refrigerated overnight to allow time to purge the soil in the gut. They then were rinsed slightly with water, blotted on paper toweling, placed into decontaminated jars, and frozen. Earthworms a n d soils were frozen to retard microbiological action on residues between times of collection and chemical analysis. Metal determination using filtrates of the cleaned-up samples were made on a Perkin-Elmer 303 atomic absorption spectrophotometer. Determinations were made a t 229.0 m p for Cd, 283.3 m p for P b (with negative background a t 280.0 m p ) , 232.2 m p for Ni (with negative background a t 240.3 m p ) , and 214.0 m p for Zn. Soil samples were thawed and mixed. Subsamples were dried a t 70°C for 24 hr, ground, and passed through a 30-mesh sieve. A 1-gram aliquot was weighed into an acid-washed porcelain dish along with 5 m l of 10% alcoholic magnesium nitrate. T h e aliquot was mixed, heated on a hot plate for 30 min to dry, and transferred to a 500°C muffle for 60 min. T h e cooled sample was transferred to a 150-ml beaker with 30 ml of concentrated HC1 and heated to dryness without boiling. Concentrated HC1 (2 ml) and approximately 15 ml of water were added to the dried material; t h e solution was brought to a boil, and transferred to a 50-ml acidwashed volumetric flask. T h e cooled solui.ion was made to volume, shaken, a n d filtered through No. 40 filter paper. T h e filtrate was used for t h e final determination. Earthworm samples were thawed and blended in a Waring Blendor. A 5-gram subsample was weighed into an acid-washed porcelain dish along with 5 ml of 107% alcoholic magnesium nitrate. The subsample was mixed, dried and charred on a hot plate, transferred to a 500°C muffle, and ashed overnight. The cooled ash was wetted with nitric acid, dried on a hot plate, and returned to a muffle for 20 min. The remainder of the procedure was identical to t h a t used for soils. Known amounts of each metal were added to a1iquot.s of soils and worms and carried through the entire procedure. Results were compared to aqueous standard solutions of the same acid composition. Recoveries of Cd, Xi, Pb, and Zn averaged 99.4. 102.5, 98.8, a n d 95.2570 in soils and 89.25, 106.5, 93.25, and 89.15% in earthworms. Residues of the metals were expressed on a part-per-million ( p p m ) , dry weight basis and were not correct.ed for recovery values. T h e frequency distributions of the residues of all metals were positively skewed. Similar results have been observed for pesticide residues in soils and earthworms (Gish, 1970: Wheatley and Hardman. 1968). but logarithmic transformation corrected some of the skewness (Heath, 1967). For this reason all metal residues .were transformed to logarithms for statistical evaluation. Results and Discussion T h e highest concentrations of metals in soils and in earthworms along either highway were found in the plots
closest to the roadway (Table 11). Concentrations in both media tended to decrease with increasing distance from the roadway, significantly so ( p
