Pergamon

Chemosphere, Vol. 33, No. 12, pp. 2475-2486, 1996 Copyright 0 1996 Elsevier Science Ltd

Printed in Great Britain. All rights reserved PII: s0045-6535(%)00348-7 00456535/96 $15.00+0.00

EFFECTS OF pH ON THE TOXICITY OF CADMIUM, COPPER, LEAD AND ZINC TO

FOLSOML4 CXNDZDA WILLEM, 1902 (COLLEMBOLA) IN A STANDARD LABORATORY TEST

SYSTEM.

Richard D. Sandifer ?? and Stephen P. Hopkin.

Ecotoxicology Group

School of Animal and Microbial Sciences

University of Reading

PO Box 228, Reading

RG6 6AJ

TelNo. 0118 931 6049

FaxNo. 0118 931 0180

E-mail: szrsandi@reading.ac.uk

(Received in Gemnny 12 June 1996: accepted 29 August 1996)

ABSTRACT

E&s for cadmium, copper, lead and zinc were determined for juvenile production of Folsomia candidu at

pH6.0, 5.0 and 4.5 in a standard laboratory test system In contrast to most previous studies where metal

toxicity was increased at low pHs, in our experiments there was no clear relationship between soil acidity and

ECSO-nproduet,on in this species. The ECSO_reproductlon values (pg g-l) for cadmium and zinc were similar at all three

pHs (pH6.0: Cd 590, Zn 900; pH5.0: Cd 780, Zn 600; pH4.5: Cd 480, Zn 590). In contaminated field sites

adjacent to primary zinc smelters, zinc is invariably present in soils at concentrations of at least 50 times that of

cadmium. Thus deleterious effects of mixtures of these metals on populations of Collembola in such sites can

be attributed to zinc rather than cadmium. Copyright 0 1996 Elsevier Science Ltd

INTRODUCTION

The bioavailability and toxicity of chemicals to soil animals are influenced by physical factors that determine

soil pore water concentrations (Van Gestel, 1992). For metals, toxicity and bio-concentration f&ctors (BCFs)

are affected by soil characteristics that influence availability, for example the pH, cation exchange capacity

2475

2416

(CEC), clay content and the percentage organic matter content (Ma et al, 1983; Van Gestel & Van Dis, 1988).

Metals are found in eight hactions within the soil: i) t&e metal cations (e.g. Pb”); ii) inorganic complexes (e.g.

CdCl’), iii) organo-metal complexes (e.g. (CH3) 4Pb); iv) organic complexes, chelates; v) bound on high

molecular weight organic material, vi) bound as diverse colloids; vii) adsorbed on colloids; and viii) within the

soil particles (Martin & Bullock, 1994). The metals in the first four of these Imctions are in the soil solution

and are more available than those bound to the soil matrix. Therefore, any soil factor that changes the relative

distributions of metals between Imctions will alter their bioavailability and hence toxicity and BCFs. In general,

lowering the pH of a metal-contaminated soil increases the toxicity to soil organisms (Crommentuijn, 1994;

Hopkin, 1989; Spurgeon & Hopkin, 1996; Walker et al, 1996).

In this paper, the effects of diierent soil pH on the toxicity of cadmium, copper, lead and zinc to the

springtail Folsomia candida has been examined in a standard laboratory test system. The aims of the study

were a) to establish whether the metals were more toxic in more acid soils, and b) to determine the relative

toxicities of cadmium, copper, lead and zinc and to compare these values to ratios of the elements in

contaminated field soils in the vicinity of a primary smelting works at Avonmouth, Southwest England where

all four metals occur together in a “cocktail” (Hopkii & Hames, 1994).

MATERIALS AND METHODS

Artificial soil was used as described in the OECD standard earthworm test Guideline 207 (OECD, 1984) and

the dra8 recommendation for the Folsomiu candidu standard test (Riepert, 1993). The medium consisted (by

dry weight) of 70% sand, 20% clay (kaolin clay) and 10% organic matter as Sphagnum peat. For further

details, see Spurgeon et al (1994). The pH of the medium was adjusted to either 6.0, 5.0 or 4.5 * 0.05 at the

start of the experiment with powdered calcium carbonate. The constituents for the artiticial soil were air- dried,

mixed thoroughly, and weighed into plastic boxes (275xl55x95mm). Solutions of cadmium nitrate

(Cd(N0&.4HrO), copper nitrate (Cu(N0&.3HrO), lead nitrate (Pb(NO,)r) and zinc nitrate (Zn(N03)2.6H20)

(BDH chemicals, Poole, Dorset, UK) were mixed with the dry constituents to give the required percentage

water content (c.30%) and metal concentrations in the soils. The same volume of distihed water was added to

the controls. The concentrations of metals used in the pH6.0 test (in pg metal g-’ dry weight of soil) were; 5,

20, 80, 300 and 1200 (cadmium); 10,40, 200, 1000 and 3000 (copper); 100, 400, 2000, 5000, 8000, 10000

and 50000 (lead); and 100, 190, 350, 620 and 1200 (zinc). At both pH5.0 and pH4.5, the same concentrations

were used for cadmium, copper and lead, but for zinc, the concentrations 100, 300, 1000, 2000, 3000, 6500

and 10000 were employed since some reproduction was still observed at 12OOpgZn g-’ at pH6.0.

Consequently, an additional experiment was carried out at pH6.0 with zinc to con&m the lack of reproduction

2477

at and above 2OOOugZn g-t. Niic acid digests of samples of contaminated soils were analysed by atomic

absorption spectrometry (for further details see Hopkin, 1989). Concentrations of metals were within 10% of

the nominal values in every case. After equilibration for 48 hours, soils were added to 2OOml plastic vending

machine cups (30g into each, four replicates for each concentration) and 5mg of dried yeast was placed in each

as a food source for the Collembola.

Cultures of Folsomiu cundidu (Wflem) were maintained in the laboratory at 20 f 1°C under constant light, in

plastic containers with a base of plaster of Paris mixed with graphite powder. A small amount of dried yeast

was added weekly as a food source. All the F. cundidu used in the test were members of a “Reading strain”,

derived thorn a single female isolated from a culture donated by Dr. J. Wiles of Southampton University. Ten

adult springtails of equal size were added to each container using a pooter. The lid of a petri dish was lightly

sprayed with distilled water and placed over the top of each cup to maintain high humidity in the containers.

The tests were all carried out at 20 f 1°C under constant light conditions. The petri dish lids were sprayed

every 48’ hours with distilled water and another Smg of yeast placed in each experimental container after two

weeks.

After four weeks the containers were flooded with distilled water and photographed individually from above

on Fujichrome Provia colour transparency slide film. The transparencies were projected onto a desktop viewer

and the number of juveniles produced, and adults surviving in each container, were counted. ECso values for

reproduction (the concentration of metal at which juvenile production was reduced to 50% of the controls)

were determined for each metal treatment at each pH from the graphs (Figs. 1,2,3). Student t-tests were

performed to determine the significance of differences in the responses of F. cundidu between control and

metal-treated soils at the three pHs (Tables 1,2,3). The pHs of the soils were measured at this stage.

RESULTS

Cadmium. At all three pH levels, a clear reduction in reproduction was observed at 1200 ug g”, whereas at

300 pg g-’ there was little effect. Adult survival was less sensitive to cadmium (Tables 1, 2, 3, Figs lA, 2A,

3A). ECSO-~~~~~~,~ values were similar in the three treatments (Table 4).

Copper. There was no reproduction at soil concentrations of 3OOOpg g-’ at all three pHs (Figs IB, 2B, 3B),

though at both pH6.0 and pH5.0 there was evidence of decreased juvenile numbers at 1OOOpg g-’ (Tables 1,2).

A slight reduction in adult survival also occurred at the highest concentrations. EC~~_~~rod~~j~ values (Table 4)

were almost identical at pH6.0 and pH5.0, but copper was less toxic at pH4.5.

2478

Table 1. Adult survival and juvenile production (mean k standard errors; 4 replicates at each concentration) for each metal at pH6.0 (ns = not significantly different Corn the control; * = significantly different fkom the control at the 5% level;** =

80 :; gY1 200 61; 7n7s4 2000 71; 6;sO 350 71; 504s8 (kO.8) (f52) (fo.6) W7) (kO.7) (f134 (fo.8) (f57)

300 816 7?6 1000 5: 2;” 5000 4?s8 2”; 620 61; 5ngsq (M.4) (f42) (fo.8) (f46) (fo.5) (&IS) (fo.3) (SO)

??* 1200 7?“s ;: 3000 3: (zl) 8000 31;

??* (& 1200 G 2:7

(M.6) (f8.8) (f1.5) (fl.1) (fo.4) (f35) ns ??* ns ** **

10000

3

(f1.3) (& 2000

;.“s *t

(fo.3) (G

50000 4l”s

** * **

0 3000 4.8 (fo.7) W) (fl.1) (i)

ns ??*

6500 ;“o

**

(fl.1) (& * **

10000 0.8 W.5) (G * **

Lead. No reproduction occurred at pH6.0, 5.0 and 4.5 at soil concentrations of 8OOOpg g” (Tables 1, 2, 3;

Figs. lC, 2C, 3C). Lead was more toxic to reproduction at pH5.0 than at pH4.5 or 6.0. E&reproductim values

(Table 4) showed no clear relationship with pH.

Zinc. At all three pHs, there was little or no reproduction at or above 2OOOug g-’ and evidence of reduction at

12OOug g-’ at pH6.0 (Table 1; Fig.lD) and 1OOOug g-’ at pH5.0 and 4.5 (Tables 2,3; Figs. 2D,3D). E&.

2479

nmwim values (Table 4) showed a slight tendency for zinc to be more toxic at lower pH values but this was

not significant.

Table 2. Adult survival and juvenile production (mean f standard errors; 4 replicates at each concentration) fur each metal at PI-IS.0 (ns = nut significantly diflkrent tican the control; ??= significantly diflizrent from the control at the 5% level;** =

IlS

80 8 26q5.3 200 6:ss 3lz5 2000 71ss 1 *rY.5 1000 3: ns

(jzO.7) (rt14) (N.8) (rt29) (N.8) (*25) (rtO.9) (*:6)

300 81; ?? **

15ngs.5 5000 71; ?? ** ??*

370 1000 6.5 38.5 2000 5.3 (kO.6) (*26) (k0.3) (k14) (*1.2) (*Is) (il.3) (:;I,)

1200 :“8 llS * *

(f1.2) (JL) 3000 3.8

(k1.3) (A) 8000 81;

**

(hO.6) (:) 3000 51;

**

(hl.0) (Z5) DS ** I( ??*

10000 71; **

(G 6500 7:“o

**

(hO.9) @1.3) (i)

50000 31; **

10000 3: **

@l.O) (Z) ??* ** (*0.5) (& ! ** ??*

Effect of pH. There were no clear relationships between adult survival or juvenile production and soil pH.

However, there was an overall decrease in reproduction in the control samples at pH5.0 and 4.5 in comparison

to those at pH6.0 (Tables 1,2,3). The mean pHs of the soils measured at the end of the experiment were 5.84

(pH6.0), 5.08 (pH5.0) and 4.54 (pH4.5).

Relative Toxicities of Metals.(Table 5) At pH6.0, the effects of cadmium, copper and zinc on reproduction

were similar, whereas lead was about five times less toxic than cadmium. At pH5.0, the toxicities of all four

metals were similar. At pH4.5, although cadmium and zinc were of similar toxicity, copper and lead were less

toxic than cadmium.

2480

Table 3. Adult survival and juvenile production (mean f standard errors; 4 replicates at each concentration) for each metal at pH4.5 (ns = not significantly different from the control; * = significantly different from the control at the 5% level;** =

80 6”.“5 3n2s3 200 E 2n4s6 ns

2000 E 2Y* 1000 3: (kO.6) (*17) (*0.6) (*34) (hO.6) (AS) (LtO.3) (+Yl)

300 6: 2”56

*

1000 7.8 2;“o 5000 71”o ns ??* .*

2000 3.8 (+0.4) @49) (+2.5) (hi4) (&0.7) $2) (*0.8) $6)

3:“s

ns ns ** ?? .*

1200 (M.6) (!c%)

3000 5Yl (d.6) (i)

8000 7”.; (MI.9) (ii)

3000 5.8

W.9) (G * ??* ns **

10000 61;

** ?? **

(iI) 6500 7.8

(a.1) (d.3) (i)

50000 i;

** ?? **

(i) 10000 3.3

(hO.8) (hO.3) (i) ns ** ** **

Table 4. E&O__& values in pg g-’ for each metal at all three pH levels, derived t?om the graphs shown in Figs. 1,2 & 3.

Table 5. ECSwU6 values of copper, lead and zinc relative to cadmium (

EC50 for metal (pg g-‘)

EC50 for cadmium (pg g-‘)

Cadmium Copper Lead ZiiC

pH6.0 1 1.20 5.03 1.53

pH5.0 1 0.91 1.75 0.77

pH4.5 1 3.06 6.56 1.22

2481

.* 4

I’

,’ ,

a’..

??.._

2482

I

f G

t

H

20 -

-

IO --

I 10

10

0 10

00

1000

0 C

adm

ium

cm

cmtra

tioa

(pg

g-l).

C) L

ead.

120

T

20 t

\

ON I

10

100

1000

lo

o00

looo

oo

Lead

con

cent

ratio

n (p

g g-

l).

L

B) C

oppa

.

80 -

-

60 -

-

‘. 40

--

20 -

-

I 1

10

100

1000

10

000

Cop

per

cmce

ntra

tim

(pg

8’).

D) Z

inc.

80 -

-

70 -

-

60 -

- 50

\

-- i

40 -

-

10

100

1000

1000

0 Zi

nc cm

cent

ratic

m

(pg

g-l).

Figu

re 3

. Adu

lt su

rviv

al

and

juve

nile

pr

oduc

tion

at p

H4.

5 ex

pres

sed

as a

per

cent

age

of th

e co

ntro

l

2484

DISCUSSION

Previous work has suggested that reducing soil pH increases metal toxicity. Spurgeon & Hopkin (1996)

exposed the earthworm Eisenia fetidu to increasing concentrations of zinc in artificial soils. They calculated

EC50 values for cocoon production of 462, 343 and 189pgZn g-’ at pH6.0, 5.0 and 4.0 respectively.

Crommentuijn (1994) used pH levels from 7.29 to 3.12 and found a range of EC50 values for total survival of

F. cundidu of 306 to 102ngCd g-’ respectively. Crommentmjn et al (1993) found an ECS+,~~~,~ value of

227 pgCd g“ at pH6.0. Whilst the figures presented in the present study are higher than the above values,

Crommentuijn et al (1993) also found an LCso value of 893pgCd g” which is not exceeded here. However,

other work has shown that in eqrimentally manipulated field soils, the abundance of some Collembola

(notably Folsomiu quudrioculutu) increases with a decrease in pH (Hagvar & Abrahamsen, 1980).

The results described in this paper show no clear relationships between the pH of soils and the toxicity of

cadmium, copper, lead and zinc to F. cundidu. This unexpected fmding demonstrates that caution should be

exercised when formulating conclusions based on the results of standard tests before they have been conducted

in several laboratories. Factors including source of OECD soil components (Riepert, 1993), and clonal

difference may influence the outcome. For example the cladoceran Duphniu magna has been found to have a

range of L&J values for cadmium of 0.06 pg g*’ to more than 1OOpg g-’ depending on which of eight different

clones is tested (Baird et al, 1990). Crommentuijn et al (1995) found an LCSO range of 802 to more than

2024pgCd g” for four different clones of Folsomiu cundidu.

However, the standard test is appropriate for determining relative toxicities of metals to F. cundidu, and

possibly other species of Collembola (Hopkin, in press). This information can then be used in attempts to

identify the most toxic metal within a “cocktail” of elements. For example, in the vicinity of the Avonmouth

smelting works, the mean ratio of Cd:Cu:Pb:Zn in soils is 1:7:50:93 (Spurgeon & Hopkin, 1995). At pH5.0

(typical of Avonmouth soils near the smelter), the toxicity of cadmium, copper and zinc to F. candidu is very

similar (in the Laboratory, lead is less toxic than these three metals, Tables 4 and 5). Since zinc occurs in

Avonmouth soils at more than ten times the concentration of copper, and nearly 100 times the level of

cadmium, it is clear that deleterious effects of the metal pollution on soil Collembola are most likely to be due

to zinc poisoning. This is clearly the case for snails (Laskowski & Hopkin, 19964 1996b), woodlice (Hopkin &

Hames, 1994) and earthworms (Spurgeon & Hopkin, 1995; Spurgeon et al, 1994) which are absent close to

the Avonmouth smelter due to the heavy zinc contamination.

2485

ACKNOWLEDGEMENTS

This work was funded by a NERC Industry Targeted Studentship with additional support Tom National

Power Plc, and the Institute of Terrestrial Ecology at Monks Wood. Aspects of the work were funded by a

grant from the Leverhuhne Trust.

REFERENCES

Baird, D.J., Barber, I. & Calow, P. (1990). Clonal variation in general responses of Duphnia magna Straus to

toxic stress. I. Chronic life-history effects. Functional Ecology, 4,399-407.

Crommentuijn, T. (1994). Sensitivity of soil arthropods to toxicants. PhD thesis, Free University, Amsterdam.

Crommentuijn, T., Brils, J., and Van St&en, N.M. (1993). Intluence of cadmium on life-history

characteristics of Folsomia candida (Wiiem) in an art&al soil substrate. Ecotoxicologv and Environmental

Safety, 26,216-27.

Crommentuijn, T., Stab, J.A., Doornekamp, A., Estoppey, 0. and Van Gestel, C.A.M. (1995). Comparative

ecotoxicity of cadmium, chlorpyrifos and triphenyltin hydroxide to four clones of the parthenogenetic

collembolan Folsomia cundida (Willem) in an artiticial soil. Functional Ecology, 9,734-42.

Hagvar, S. & Abrahamsen, G. (1980). Colon&ion by Enchytraeidae, Collembola and Atari in sterile soil

samples with adjusted pH levels. Oikos, 34,245-58.

Hopkin, S.P. (1989). Ecophysiology of Metals in Terrestrial Invertebrates. Elsevier Applied Science, Barking.

Hopkin, S.P. (in press). Biology of the Springtails (Znsecta: Collembola). Oxford University Press.

Hopkin, S.P. & Hames, C.A.C. (1994). Zinc, among a “cocktail” of metal pollutants, is responsible for the

absence of the terrestrial isopod Porcellio scuber fiorn the vicinity of a primary smelting works. Ecotoxicology,

2. 68-78.

Laskowski, R. & Hopkin, S.P. (1996a). Accumulation of Zn, Cu, Pb and Cd in the garden snail (Helix

aspersa): implications for predators. Environmental Pollution, 91, 289-297.

Laskowski, R. k Hoplcin, S.P. (1996b). Effects of Zn, Cu, Pb and Cd on titness in snails (Helix uspersu).

Ecotoxicoiogy and Environmental Safety, 34, 59-69.

2486

h4a, W. C., Edelman, T., Van Beesum, I. and Jans, T. (1983). Uptake of cadmium, zinc, lead and copper by

earthworms near a zinc-smelting complex: influence of soil pH and organic matter. Bulletin of Environmental

Contamination & Toxicology, 30,424-427.

Martin M.H. & Bullock, RJ. (1994). The impact and fate of heavy metals in an oak woodland ecosystem In:

Ross, S.M. (Ed.) Toxic metals in soil-plant systems. John Wiley, Chichester, U.K. pp. 327-365.

OECD (1984). Guidelines for the testing of chemicals No. 207 Earthworm acute toxicity tests. O.E.C.D.

Adopted 4 April 1984.

Riepert, F. (1993). IS0 ring test of a method for determining the effects of soil contaminants on the

reproduction of Collembola. Report for: Biologische Bundesanstalt fbr Land- und Forstwirtschaft.

Spurgeon, D.J. & Hopkin, S.P. (1995). Extrapolation of the laboratory-based OECD earthworm toxicity test

to metal-contaminated field sites. Ecotoxicology, 4, 190-205.

Spurgeon, D.J. & Hopkin, S.P. (1996). Effects of variations of the organic matter content and pH of soils on

the availability and toxicity of zinc to the earthworm Eisenia fetida. Pedobiologia, 40, 80-96.

Spurgeon, D.J., Hopkin, S.P. & Jones, D.T. (1994). Effects of cadmium, copper, lead and zinc on growth,

reproduction and survival of the earthworm Eisenia fetida (Savigny): assessing the environmental impact of

point-source metal contamination in terrestrial ecosystems. Environmental PoNution, 84, 123-130.

Van Gestel, C.A.M. (1992). The influence of soil characteristics on the toxicity of chemicals for earthworms: A

review. In: Greig-Smith, P.W., Becker, H., Edwards, P.J. & Heimbach, F. (Eds.) Ecotoxicology of

Earthworms. Intercept, Andover, U.K., pp. 44-54.

Van Gestel, C. A. M. and Van Dis, W. A. (1988). The influence of soil characteristics on the toxicity of four

chemicals to the earthworm Eisenia andrei (Oligochaeta). Biology &Fertility of Soils 6,262-265.

Walker, C.H., Hopkin, S.P., Sibly, R.M. & Peakall, D.B. (1996). Principles of Ecotoxicology. Taylor &

Francis, London.