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378

THE LETHAL ACTION OF SOLUBLE METALLICSALTS ON FISHES

BY KATHLEEN E. CARPENTER, PH.D., M.SC.

(Department of Zoology, University College of Wales, Aberystwyth.)

{Received 2nd February 1927.)

(With Three Diagrams.)

A. INTRODUCTION AND DETAILED INVESTIGATION OF THEACTION OF LEAD-SALTS ON FISHES.

THE work of several years on the fauna of streams polluted by lead-mining(1, 2, 3)has revealed the fact that the destruction of fish-life in such streams is neither amatter of starvation nor emigration for lack of food, nor of spawn-destruction, butis a direct consequence of the action of lead-salts in solution (probably as thesulphate) upon the fishes themselves. Further, experiments both in the field (usingfish cages in the polluted streams) and in the laboratory (using filtrates of the floodwaters and chemical solutions) have clearly demonstrated that one part of lead inthree millions of water may be lethal to minnows, sticklebacks and trout. It seemedworth while, therefore, to investigate the physiological nature of the reaction inorder to discover whether it followed the normal course of a toxic reaction.

The principal work available for comparison is that of Powersu, 5), who, byworking with a great variety of substances toxic to fishes, has been able to formulatecertain general conclusions which hold good for all except three anomalous caseswhich will be mentioned later. His method is to place fishes in a standard volumeof solutions of the substance to be tested at different degrees of normality and todetermine the length of time which elapses before death. This, the survival-time,is plotted graphically against the concentration, the interpolated curve being the"survival-curve" (see Diagram I). This curve is very constant in form, and "re-sembles an equilateral hyperbola," a certain portion of the horizontal limb beingalmost a straight line. Since the actual incidence of fatality stands in inverse re-lation to the survival-time, the reciprocals of the survival-times (calculated as 100/t,to avoid fractions) are plotted to give a curve known as the "velocity of fatalitycurve." This curve, also, is very constant in form, being typically sigmoid, asappears on the diagram, i.e. the velocity of fatality increases with the concentrationmost rapidly in its middle portion, which corresponds in the general run of casesto the 45-210 minutes section of the survival-curve. Powers explains the char^Ain slope of the curve by the statement that a weak toxic solution tends to acceleratethe general metabolism of the subject, while a very strong one retards it, and that

Lethal Action of Soluble Metallic Salts on Fishes 379

e alterations have a reflex influence on the rate of the original toxic action.the production of the straight line portion of the velocity of fatality curve is

achieved the "theoretical velocity of fatality curve"—a straight line which cutsthe abscissa at a point designated as the "theoretical threshold of toxicity." Thispoint indicates the degree of concentration below which toxic action fails, or is atany rate feeble and uncertain, survival-times being protracted and variable.

The horizontal limb of the survival-curve corresponds in general to the equation

y (x - a) = K,where y is the survival-time,

x is the appropriate concentration,a is the theoretical threshold concentration,

and K is a constant dependent upon the toxic substance employed.The speed of the reaction also varies, roughly speaking, inversely according to thesize of the fish, and directly according to the temperature.

From the variety of toxic agents employed by Powers, it may be concludedthat this is the standard form for a toxic action upon fishes.

By this standard I have attempted to test the action, first, of lead, later, of othermetallic salts.

Powers' experiments were made upon the goldfish Carassius carassius: my ownearly work had shown that the action of lead-salts was constant in type towardsall the freshwater fishes employed, viz. trout, minnows, sticklebacks and goldfish,but most rapid with minnows and sticklebacks, slowest with goldfish. I, therefore,resolved to use minnows .{Leuciscus phoxinus) as my standard type, as they arefairly easily obtained and are easily kept in the laboratory. Early experience alsoshowed that all the soluble salts of lead produced very similar effects: it wasdecided to use the nitrate, Pb(NO3)2, as an inorganic and readily soluble form.

A series of experiments on the model of Powers' work with NaCl gave a curvevery similar to his original survival-curve, only thrown back slightly towards theorigin—this I take to indicate "the greater susceptibility of minnows as comparedwith goldfish, especially as these experiments were run at a temperature of only180 C , those of. Professor Powers at 21-5° C. The reciprocal curve gave thetheoretical threshold of toxicity concentration as about 0-15 N, as compared with0-25 N for Carassius, and the straight-line portion of the survival-curve as far asc-33 N agreed with the equation K = y (x — a), K being in this case 7-0 (seeDiagram I). The specimens used in the series of experiments which form thebasis of Tables A to C, were, with three exceptions, young males, sexually mature,of about i | to 2J inches in length and about o-8 to I-I gm. in weight, captured inearly summer as soon as they came up, preliminary to the spawning season, tothe marginal shallows of an upland pool. (The three exceptional cases were females

l<about the same size, carrying ova.) They were thus at the height of physio-Ical condition. During the whole course of my experiments, not a single one

of my stock has died. Controls have been kept—one was retained for five weeks—without loss, in water distilled in the same tank as that used in making up the lead

38o KATHLEEN E. CARPENTER

solutions: the possibility of toxic action on the part of the distilled water itselfseems thus to be eliminated. Determination of the actual death point present*no difficulty: there was always a preliminary phase of violent leaping and darting,beginning about 10 or 15 minutes before death, while a final phase of convulsiveshuddering of the whole body, and particularly of the fins, occupied the last twoor three minutes (never longer), the fish lying meanwhile on its side.

700 -

600 -

500 -

400 -

300 -

200-

100 -

Reciprocate*/~wr4

0-1 0-2 0-3 0-4Concentration (normality)

- 1

0-6N

Diagram I. Toxicity of NaCl toX X

(a) Carassius carassius (after Powers) —X X

and to (b) Leuciscus phoxinus (original) — — —•• —

*—x' is the Velocity of Fatality Curve, andy—y' the Theoretical Velocity of Fatality Line, of Powers.

For goldfish of usually 3 to 4 gm. weight, Powers used a standard volume of2 litres of the toxic solution: for minnows of usually less than 1 gm., I used atfirst a standard volume of 500 c.c. The temperature was kept nearly constant at16-5 to 17-5° C.

The result of such standardised experiments was the production of a verysmooth survival-curve (Diagram II), which can be constructed from Table^This is an actual point-to-point curve derived by interpolation between poinfixed by the mathematical averages of a double series of experiments. The velocity


fatality curve was plotted on the reciprocal basis according to Powers' method—p t h the result that the theoretical velocity line was found never to cut the baseline at all, i.e. there was no theoretical threshold of toxicity concentration. Thismight be interpreted at its face value as denoting that the lethal capacity of lead,considered as a toxic agent towards minnows, is infinite, i.e. that no concentration,however low, can fail to have a toxic action—a conclusion which seems in goodagreement with the practical findings mentioned. But closer inspection of thesurvival-curve reveals features of unusual interest: even superficially it is of un-

500

002 0-04 0-066005 0-08

0-16 0-18 0-2N0-1 0-133

Concentration (normality)

Diagram II. Survival-curve of Leuciscus phoxinus in lead nitrate solutions.a'—a shows survival-times in 500 c.c. volumesV—a shows survival-times in large (3000 c.c.) volumesb'—a is also the graph of theoretical values of t in the equation

K = - log , when K = o-o\3.t cone.

x—x' and y—y' are as in Diagram I.

familiar form—not only is it pushed back towards the origin, indicating a remark-able efficacy of lead at low concentration, but it is certainly not a rectangularhyperbola, nor does any portion of it conform to the equation K = y (x — a),taking a (the threshold of toxicity concentration) as o. Again, the experimentalvelocity of fatality curve, not being sigmoid in form, does not fulfil the theoreticalrequirements. Undoubtedly this is not the standard curve of a toxic reaction, asestablished by Powers.

It does, however, correspond very well along tne greater part ot its course toequation of a different type, which may be expressed as

„ 1, 1K = - log ,t 6 cone.

382 KATHLEEN E. CARPENTER

where t = survival-time, and K = 0-013 at the given temperature. (See Tableand Diagrams II and III.)

Table A. Action of lead nitrate solution (500 cc. volumes) on Leuciscus phoxinusat a temperature of i6-5o-iy5° C.

Concentra-tion

(normality)

O-20

o-i8

o-i6

0133

o-io

0-08

0-066

0-05

0-025

O-O2O

0-016

0-0133

o-oi

0-008

0-005

O-OO2

o-oo 1

0-00025

o-oooi

Weightoffish(gm.)

o-61-051-310-76o-8I-2II-OIo-6io-860-92o-86

089*0-99o-8i0-720-75*

0-79o-860-700-690-740-90093099o-8o0-90o-661-050-85o-86I-I2*0-830-85O'9O0-850-85'

Survival-time

(mins.)

III58170J65170/70185}721

IOIj901

120I128J1751210J1951215J2051275 (2591305/2651345 J3201325)365400 J4751560J675+1690 J7601890)

" 8 5 I1290J

Averagesurvival-time

(mins.)

53-5

54

64

67-5

77-5

86-s

102-5

1 2 4

192-5

2 0 5

2 4 0

282

305

322-5

382-5

517-5

682; -5

825

1237-5

Reciprocal

(4s)1-87

1-85

i-6

i -5 -

i - 3 -

1 1 5 -

0-97

o-8o

0-52+

0-49-

0-41+

O-35+

O-33"

0-31+

0-27

O-2-

0-14+

O-I2+

0 0 8

Value of K/ 1 * \^ = l l 0 g c ^ c " J

0-0128

0-0136

0-0137

0-0127

0-0129

0-0127

—

—

—

—

—

. —

—

—

—

—

—

—

—

• In the three cases indicated, females carrying ova were used in place of mature male fishes.

The curves diverge in the region of concentration 0-06 Af, the discrepancy in-creasing steadily as the concentration diminishes. An explanation of this apparentdiscrepancy was afforded by a series of experiments in which a number of minnowswere killed successively in one and the same 500 cc. sample of c-i N lead nitratesolution: the survival-time was found to be prolonged with each successive ex-periment, until finally the eighth fish, of practically the same size and weight asthe first (about 0-5 gm.), had a survival-time of nearly double the standardThe actual survival-times were, in order, 73, 89, 92, 93, 94, 120 and 130The deduction was obvious: the solution was progressively weakened by theabstraction from it of a certain proportion of the lethal substance by each fish


, and the lethal efficacy was thus progressively reduced. In a solution oflow concentration, the depreciation even during the survival-time of a

single fish would be considerable: larger volumes of the weaker solutions should,therefore, be employed in order to obtain the maximum effect. A few tests withlarger volumes showed that with concentrations not lower than 0-06 N a volumeof 500 c.c. was adequate for the maximum effect, but below this concentration

Table B. Survival-times (Leuciscus phoxinus) in 3000 c.c. volumes of Pb(NO3)2

solutions, compared with the values of t as calculated from the equation

when K= 0-013.

K= -logt ° cone.

Concentration(normality)

O-2

o-i8

o-i6

0-133

o-i

o-o8

0-05

0-04

0-02

o-oi

0-005

Weight of fish(gm-)

0 61 051-310-76o-8I-2II-OIo-6io-860-92o-86

0-741-20-76o-8i -o0-920-710 8 90-69o-86

Survival-time(mins.)

8}SI58}70)65}.70/70185)72)

101/95}97/

iiol1 1 1 /I I *» }

134/iiol190/150)208/

A t tAf n f9^±

Average

53'5

54

64

67-5

77'S

88-s

96

110-5

124-5

150

179

Calculatedvalue of t

53-8

569

61

67-3

77

84-3

1 0 0

1075

130Q

153-8

177

the survival-times were very considerably shortened by the employment of largevolumes. Table B gives the corrected survival-times, obtained by the use of3000 c.c. volumes of the solutions, for comparison with the theoretical value of t,as calculated from the equation

„ 1, 1K= -logt °cone.

Further, the lethal efficacy of the solution was found to vary in inverse pro-portion to the actual size of the fish employed, as well as directly according tothe absolute quantity of the lead-salt; thus, the minimum absolute quantity of

ad (as Pb) required to kill fishes between 0-75 and o-8o mg. in weight and if—I^Fs in length was between 0-025 and 0-05 mg. (Pb); for fishes of above 2|- inches

and 1-40 mg., o-io mg. Pb was insufficient (cp. Huxley's observations on the actionof mercuric chloride—another heavy metal salt—on Mytilus gill-tissue (6)).

3*4 KATHLEEN E. CARPENTER

The direct dependence of lethal action upon the absolute quantity of thesalt, together with the discrepancy between the equation expressing thisand Powers' standard equation for a toxic reaction whose rate is affected by altera-tions entailed in general metabolic processes, suggested that the entire quality ofthe lead-reaction might be of a type not hitherto described, and an attempt wasmade to discover the exact nature of this process, as well as the precise factor whichdetermined it.

In the case of the latter: it is well known that certain metallic salts, whenionised in water, may produce definitely acid solutions, and that the mere presenceof an unusual concentration of hydrogen ions in the watery medium may be fatalto aquatic species, and definitely harmful to fishes in particular(7).

Table C. Action of dilute nitric acid on Leuciscus phoxinus, tabulated for comparisonwith the action of lead nitrate solutions at corresponding degrees of hydrogen ionconcentration.

Lead nitrate


O-2o-i60 1 00-05o-oz0-005

Survival-timeoffish

(mins.)53-564ITS96

130177

pH

4-4

4-8

S-8J

Nitric acid

Survival-time

(hrs.)77^7i7i

274-28Over 3 days, without ap-parent effect. Presumablyno lethal action

The hydrogen ion concentration of the water of the pool from which theminnows were taken was found by the colorimetric method to be pH 6-4; that ofthe distilled water used for making up the lead-solutions and also for the control-experiments was also pH 6-4 (a detailed analysis of a sample of this distilled water,for which I am indebted to Mr John Evans, Public Analyst to the County ofCardigan, showed it to be of a high degree of purity); the hydrogen ion concen-trations of the lead nitrate solutions (see Table C) ranged from pH 4-4, at cone.0-2 N, to pH 5-6 at cone. 0-005 -W. It was, of course, impossible to buffer downthe solutions without inducing precipitation of the lead; however, a series ofexperiments were carried out, using very low concentrations of nitric acid, todetermine how far the alterations in pH might be supposed to be a factor in thelethal action observed. The results, summarised in Table C, showed that a solutionof nitric acid at pH 4-4 kills in about 7 hours, one at pH 5-0 in about 27 hours,while at pH 5-4 and below there is apparently no lethal action whatever. A com-parison of these figures with the survival-times of minnows in lead nitrateat corresponding concentrations of hydrogen ion appears to indicate clearlyalthough the metallic solutions employed are in some cases so acid as to be harmfulto the fishes on this score alone, yet the effective lethal action, as measured by the


«vival-times, is directly conditioned by the concentration of the metallic ion, toich it is in accurate proportion.This being so, it remains to determine the exact part played by the metallic

ion in the lethal process. The symptoms exhibited by the fishes, both ante- andpost-mortem, were peculiarly interesting: in all cases a phase of uneasy dartingwas succeeded by a period, usually protracted, of relative quiescence, during whichthe fish floated almost inert at the surface of the water, with irregular, jerky move-ments of jaws and operculum which seemed to indicate respiratory distress, whilethe body became coated with a thin and Veil-like film, which looked like coagulatedmucus. Within the operculum, the gills were seen to be covered by a thicker film,or pad, of apparently similar nature, and when, after death, the body was immersed,after washing in distilled water, in a weak solution of ammonium sulphide, thisfilm and pad at once assumed the black colour characteristic of precipitated leadsulphide. The whole "clinical picture" suggested death by suffocation, inducedby the clogging of the gills by a film of colloidal material formed by the interactionof the metallic ion with some constituent of the mucus. The resulting respiratory

Table D. Rate of respiration in Gastrosteus aculeatus.

Length of fish (inches)Rate of opercular movements (strokes per min.)

(average of 5-minute observations)Rate of evolution of CO2 (gm. per min.)

(average of 35-minute observations)

(a) Control—untreated fish

1A120

0-0033

(b) Fish treated inlead nitrate solution

140

0-0013

distress seemed very obvious: in order to test its reality, a few experiments werecarried out with small sticklebacks (Gastrosteus aculeatus), using two sets of fishesof about the same size, the one set being treated in dilute Pb(NO3)2 solutions until"film" was clearly apparent, the others used as controls. The rate of opercularmovements in each specimen was counted, and the rate of evolution of carbondioxide calculated by Saunders' indicator method(8). The results, a specimen pairof which are given in Table D, indicate clearly that, while the rate of opercularmovements in "treated" fishes exceeds the normal, the effective rate of gaseousexchange is far below it. Respiratory distress, conditioned by the production of"film," is thus a genuine symptom.

Whether we consider this condition to be merely symptomatic, or itself thecause of death, is another matter. The latter conclusion would seem to be stronglyindicated by the facts connected with the recovery of fishes placed in solutionscontaining a quantity of lead salt insufficient to induce death. In such cases,

«m " is formed up to a point, and there is a period of obvious respiratory distress:>very finally takes place when the film is shed (probably by continuous secretion

of mucus below it) and falls off in shreds into the surrounding medium, which isfound to be exhausted of its lead. If the supply be renewed before this shedding

BJEB-IVJV 26


takes place, the lethal action proceeds straightway to a finish; if, however,be delayed until the shedding is achieved, the whole process seems to startfrom its beginnings, like Penelope's web; it is in fact possible to renew the solutiona great number of times without bringing about the death of the subject, provideda sufficient interval be left in each case. (This, by the way, explains the difficultiesof Drs Dilling and Healey(<>), who found it possible for goldfish to survive in asolution of lead 1 : 60,000, renewed at intervals which, on the evidence suppliedby the writers, were long enough for the mucus to shed off into the water and tomake of it "a very turbid fluid," "quite free of dissolved lead.")

An experimental series designed to test the influence of a change in temperatureupon the survival-time in o-iA^ lead nitrate solution gave the following result:

The survival-time of a fish of average weight at a temperature of 120 C. was90 minutes, at 14° C. was 83 minutes, at 16-5° C. was 70 minutes, at 17-6° C. was67 minutes, at 19-2° C. was 46 minutes, at 220 C. was 40 minutes. (A minnowplaced in water and subjected to gradual heating died when the water-temperaturereached 280 C.)

There is thus over 100 per cent, difference in time in correspondence with arise of io° C. in temperature—this seems to agree with Van't Hoff's rule for therate of a purely chemical reaction.

Finally, an attempt was made to establish the amount of lead which entersinto combination with the mucus, and the amount (if any) which passes into theblood-stream, by the following method.

Two large minnows (of length about 3J inches) were placed together in a1500 c.c. volume of distilled water, to which was added o-6 c.c. of N/10 lead nitratesolution. The total quantity of lead supplied was thus 0-00621 gm., or 6-21 mg.Immediately after death, the bodies were removed and placed in a solution ofacetic acid (fairly dilute), in which they were left for four minutes, by the end ofwhich period the gills were quite clear. The bodies were washed for 10 minutesin distilled water, and this liquid was added to the acetic acid solution to constituteSample B, the original lead nitrate solution being preserved as Sample A. Thebodies were then burnt to ashes in a platinum crucible, and the ash extracted withacetic acid: the extract was Sample C.

All three samples were analysed for lead-content by the usual colorimetricmethod, the result being as follows:

Original weight of lead in lethal solution =Pb 0-00621 gm. or 6-21 mg.Sample A (original lead nitrate solution in which the fishes died) =Pb 0-0018 gm. or i-8 mg.

„ B (mucus-coat washed off and dissolved in acetic acid) =Pb 0-00462 gm. or 4-62 mg.„ C (residue: internal body-contents) =Pb nil

(This last sample gave absolutely no trace of coloration whentreated with H S )Total weight of lead, from Samples A and B =Pb 0-00642 gm. or 6-42 mg.

(Estimations were made by Mr Reginald Jones, B.Sc, Edward Davies Chemical Laboratory

There are several loopholes for experimental error, witness the slight overplus(0-00021 gm. or 0-21 mg.) in the final estimations, but in the opinion of the writer,


«conjunction with the other evidence discussed, it furnishes the final link in aFin of evidence which clearly demonstrates that the effective action of dissolved

lead-salts on fishes is not "toxic" in the ordinary acceptance of the term, as im-plying changes in internal body fluids, but is purely external in character, con-sisting in the precipitation of an organic compound of lead which clogs the gillsand inhibits their respiratory function, and thus leads to death by suffocation.

Such action is lethal in effect, however low the concentration of the salt, pro-vided it be supplied in sufficient quantity.

This low minimum-level is a very important factor in the economic considera-tion of the treatment of lead-mine-effluents for the prevention of damage to river-fisheries. The possibilities of effective treatment directed to this end have beendiscussed elsewhere (3).

B. ACTION OF OTHER METALLIC SALTS.Mention has already been made of three anomalous cases, cited by Powers, of

presumably toxic substances whose action upon goldfish, though lethal in effect,did not conform to the rules which he found generally applicable to a great varietyof toxic agents, ranging from sodium chloride to phenol and caffeine. It is re-markable that these three "anomalous cases" were those of cupric chloride,cadmium chloride, and ferric chloride—the only examples of salts of the heavymetals with which this author worked. While the curves obtained by Powers withthese salts present some surprising irregularities, capable of receiving severaldifferent interpretations, yet their general trend is such as to suggest an analogywith that of lead nitrate, newly established. Further, my own early observationson the action of soluble zinc salts (which occur commonly in the local lead-mine-effluents) indicated that death of fishes was due to an action very similar in typeto that of lead, and similarly operative at remarkably low concentrations. It was,therefore, resolved to test the action of soluble salts of the heavy metals in detail,using the standard large volumes which had been found efficacious in the case oflead nitrate. The general result was to establish a remarkable uniformity of actionon the part of all the metallic salts employed: the survival-curve in every caseapproximated closely to the equation

K = - log ,t 5conc. '

only differing in the value of K; i.e. the salts differed in rapidity of action, but eachshowed a precisely similar general type of effect, marked by the formation of"film," covering the general body-surface and thickest over the gills, which filmdarkened immediately in contact with ammonium sulphide. (In the case of cad-mium salts, the resulting precipitate was orange-brown in colour, in that of zinc,adirty pale-brown, in all the others it was black.) The usual symptoms of respi-^ V T distress were noticed in every case.

The zinc sulphate experiments were made with young male minnows obtainedfrom the same source as those used in the lead nitrate series, and at the same season

26-2


(May to June, 1926); the remaining tests were carried out in the autumnminnows obtained from a locality in the south of England. These lattera larger race than the local variety, but a few tests with lead nitrate showed themto be equally sensitive to its action. They were all in good condition, and the stockwas kept in the laboratory tank without any losses, save for one death which oc-curred in November, just as the ultimate series of experiments were being run.The constants established were as follows:

For lead nitrate at 170 C , K = 0-013„ zinc sulphate at 180 C, K = 0-013„ cadmium sulphate at 160 C , K = 0-013„ ferrous sulphate at 160 C , K = 0-013„ ferric chloride at 15° C , K = 0-018„ copper sulphate at 16° C , K = 0-040„ cupric chloride at 160 C.#, K = 0-021

• The average weight of fish in this series was very high: neglecting those above standard size wefind that, in the smaller series K =0'O4O, which is identical with the value for copper sulphate.

For mercuric chloride at 150 C , K = o-oi

The condensed results are reported in Table E and graphically rendered inDiagram II I : it will be noted that the greatest divergence from "theoretical values "of t (which even here is comparatively slight) occurs in the CuCla, FeCl3 andFeSO4 series. In the two former cases, the irregularity may be due to the colloidalpeculiarity; in the last, it is probably caused by the rapidity with which oxidationtakes place. Care was taken to reduce such causes of error to the minimum, bythe use in every case of absolutely fresh solutions, well shaken before dilution,and the results show, on the whole, very little irregularity.

The general conclusion arrived at is that the lethal action of soluble salts ofthe heavy metals on freshwater fishes consists in the formation of an insolublecompound of the metallic ion with some constituent of the mucus, which coatsover the skin and gills and finally causes death by suffocation. This action canbe lethal even at extreme dilutions, and the economic importance of such a con-clusion has already been urged by the writer, both here and elsewhere: it puts anentirely new complexion upon the question of the treatment of mine-effluents forthe preservation of river-fisheries.

The whole of this work, as well as the greater part of my pollution-studies,was carried out under a grant from the Department of Scientific and IndustrialResearch, and in the Laboratories of the Zoological Department of the UniversityCollege of Wales, Aberystwyth.

I am greatly indebted to Professor T. Campbell James, of the Edward DaviesChemical Laboratories, for chemical advice and facilities, and must also expressmy sincere acknowledgements to Professor J. S. Huxley and Mr C. F. A.for some illuminating criticism.


Table E. Average survival-times in solutions of different metallic salts.


0-2o-i60-1330-125OIO00800660-050*040-0330-020-0130010*0050-0020001000080-00050-0001

Zincsulphate

Av.t

62-567-5

13-5• 3

3o"-542-544

101-5

Theor.t

6 7 3

1001075

130

153177

Cadmiumsulphate

^=0-013

Av. Theor.t t

58 61

65 69478 7783 843

102 100

—

1805 153-9

Ferroussulphate/C«o-oi4 .

A v .

59

6368795

1035

i i i - 5

144187

Theor.t

55-6

64-57J-478-3

9 9 4

IOS-S

14291653

Ferricchloride

Av.t

4 7

SO

I?68-5

77

86895

Theor.t

4 4 2

50-155560-9

72-3

90-1

i l l127-5

Cupricsulphate

K - 0-040

Av. Theor.t t

18-5 198

22-5 225235 2527 27-4

31-5 32-5

38 38

495 5O62-5 57'5

Cupricchloride

K « 0-021

Av. Theor.t t

38-5 371

48 477

SO-5 619

725 72-5

825 952

MercuricchlorideK - O - I O

Av.t

—

—

1 2

• 55

29530

3342-5

Theor.f

—

—

13

16-9

20

26-9303093340

•005 01 02 05 -10 -16 N

Logarithms of concentrationsDiagram III. Survival-times in

ZnSO4 • FeCl3 ©CdSO, x CuSO4 +FeSO, © CuCl, 0

plotted in relation to values of K.

Minutes150-i

100-

50-

HgCl2


SUMMARY.

A. Introduction and detailed investigation of the action of lead-salts.

A study of pollution of Welsh rivers by lead-mine-effluents revealed the factthat fishes were killed by the action of soluble salts of lead, which proved lethalat concentrations so low as Pb i : 3,000,000. A physiological investigation of theaction of lead-salts revealed the following facts:

1. The action does not correspond to the normal toxic type established byPowers (4. s).

2. The graph of survival-times in different concentrations closely follows theequation

1K=\\og-{cone.

3. The speed of the reaction is dependent upon the total quantity of metallicion present, as well as upon the actual concentrations.

4. The speed of the reaction varies in inverse relation to the size and weightof fishes employed.

5. The most marked symptom is the formation of a film over gills and skin,by interaction of the metallic ion with a mucus-constituent. Death by suffocationis the final result. Where insufficient lead ion is present, the film is shed off, andcomplete recovery takes place.

6. The speed of the reaction varies in direct relation to the temperature con-sistently with Van't Hoff's Rule.

7. Chemical analysis of residues shows that no trace of metallic ion penetratesinto the body itself. The action is thus held to be purely external in process,chemical in type, and mechanical in effect; i.e. it is not a "toxic" action in theordinary sense of the term.

B. Action of other metallic salts.

The action of soluble salts of zinc, iron, copper, cadmium and mercury isshown to follow the same law as that of lead.

Attention is directed to the economic importance of the facts, in connectionwith the pollution of rivers.

LIST OF REFERENCES.(1) CARPENTER, KATHLEEN E. (1924). Ann. App. Biol. 11, 1, 1-23.(2) (1925)- Ann. App. Biol. 12, i, 1-13.(3) (1926). Ann. App. Biol. 13, 3, 395-401.(4) POWERS, EDWIN B. (1917). Illinois Biological Monographs, 4, 2, 1—73.(5) (1920). Ecology, 1, 2,9S-ii2.(6) HUXLEY, J. S. (1922). Biol. Bull. Mass. Biol. Lab., Wood's Hole, 43, 210.(7) RUSHTON, W. (1922). Ann. App. Biol. 9, i, 77-80.(8) SAUNDERS, J. T. (1923). Proc. Camb. Phil. Soc, Biol. Ser. 1, 43.(9) DILLING, W. J., HEALEY, C. W. and SMITH, W. C. (1926). Ann. App. Biol. 13, 2, 168-176.

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