Trichloroacetic acid as a phytotoxic air pollutant and the dose-response relationship for defoliation of Scots pine

The Science of the Total Environment 160/161(1995)

459-463

Trichloroacetic acid as a phytotoxic air pollutant and the dose-response relationship for defoliation of Scats pine Yrjii Norokorpi*“,

Hartmut Frankb

aFinnish Forest Research Institute, Rowniemi Research Station, P.O. Box 16, FIN-96301 Rowniemi, Finland bInstitute for Toxicology, University of Tiibingen, Wlhelmstrasse 56, D-72074 Tiibingen, Germany

Abstract

Various ubiquitous volatile organic air pollutants (VOCs), especially C,-halocarbons, may be converted to secondary air pollutants that are phytotoxic and known as herbicides. One of these is trichloroacetic acid (TCA), found in concentrations ranging from 10 to 130 rig/g in the foliage of forest trees in northern Finland. TCA has been used as a herbicide against monocotyledonous weeds. It has formative effects, inhibits growth, and induces chlorosis and necrosis of light-exposed leaves, including those of woody plant species. Twenty Scats pine trees in an experimental stand 50 km southeast of Rovaniemi were sampled for correlation of TCA levels and needle loss. The trees located at the northwesterly edge of the stand could be divided into two groups, one more resistant to the phytotoxicant TCA than the second. The range of TCA concentrations in needles was 8-65 rig/g. The extent of defoliation (range 25-90%) waslower in the TCA-resistant group, with a gradient of 0.32% defoliation per unit TCA concentration; in the sensitive group, the correlation line had a steeper slope of 0.78% defoliation per unit TCA concentration. These two groups serve as a basis for further studies on morphological, anatomical, and biochemical parameters. Airborne chlorocarbons; Forest decline; Herbicides in conifer needles; acid; Airborne haloacetic acids

Keywords:

1. Introduction Many airborne organic air pollutants (VOCs) may be activated by atmospheric oxidation to phytotoxic secondary products (Frank and Frank, 1985). For instance, the widely used C,-chlorocarbon solvents are partly oxidized to trichloroacetic acid (Frank, 1991; Frank et al., 1992b). Monochloroacetic acid is present at even

*Corresponding 004%9697/95/$09.50 SSDZ

author.

Sylwstris;

Trichloroacetic

higher levels in the atmosphere (Frank et al., 1994). Both haloacetic acids are phytotoxic, and several derivatives of these have found applications as commercial herbicides. Trichloroacetic acid (TCA) has been employed as a sodium salt or in the form of ester or amide derivatives against perennial grasses. It has formative effects, mhibits growth, and induces chlorosis and necrosis of light-exposed leaves, including those of yoody plant species (Barrons and Hummer, 1951; Aberg, 1992). Several monitoring campaigns have been per-

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formed to assess the TCA levels in conifer needles from southern central Europe to northern Europe (Frank et al., 1990, 1992b, 1994; Juuti et al., 1993). The results of a database of more than 600 analyses indicate that TCA occurs in conifer needles (fresh wt.) throughout Europe at levels between 5 and 130 rig/g. The concentrations in northern Finland tend to be higher than those in Central Europe. Correlations between TCA concentrations in conifer needles, defoliation of trees, and damage of the surface wax layer have been reported (Frank et al., 1992a,b, 1994; Pliimacher and Renner, 1992). Distinct differences in the TCA levels in the needles of uniform adjacent stands have been shown (Frank et al., 1992b), and even within a stand, the levels in individual trees can vary widely. This variation seems to be largely the result of ecological and micrometeorological factors such as wind passage, solar radiation, temperature, stand structure, spacing of trees, and local topography (Frank et al., 1992b; Norokorpi and Frank, 1993). The purpose of this study was to correlate TCA concentrations in third-year needles versus defoliation of Scats pine on a site where growth conditions of the trees were as homogeneous as possible. 2. Material

and methods

The experimental area is located about 50 km southeast of the center of Rovaniemi (66”22’N, 26”43’E). The pure Scats pine (pinus Syruestris L.) stand lies at an elevation of 160 m on a level, dryish, sandy heathland site. The field layer vegetation is dominated by Empetrum nigrum L., Vaccinium myrtillus L., Vaccinium vitis-idaea L. and Calluna uulgaris (L.) Hull. Pleurozium schreberi (Bird.) Mitt. and Cladonia species are dominant in the bottom layer. The pine trees have been regenerated naturally after a forest fire about 120 years ago. The stand density is about 280 stems/ha with a canopy closure index of 0.6 (1.0, full closure; 0, bare). The basal stem area averages 16 m*/ha. The mean tree height is 19 m (range, 16-23 m). The volume of the stand is 140 m3/ha.

160 / 161 (1995) 459-463

The material was collected in late August 1992 at the northwesterly edge of the stand, bordering a seedling stand. Twenty of the outermost trees were sampled systematically from the dominant canopy layer at a distance of 170 m along the edge. The average height of the 20 sample trees was 17.8 m (range 15.5-20.3 m>. The mean height of living crowns was 8.3 m (range 5.2-10.6 m), constituting 47% of the entire tree height. The distance to the nearest tree averaged 5.3 m (range 2.8-8.8 m). Needle loss was assessed as described by Jukola-Sulonen et al. (1990). The characteristics of branches were measured on a first-order branch sampled from the southwesterly quadrant at a height level of one-third of a living crown down from the tree top (i.e. at a height of 15-16 m above the ground). The needle samples for TCA analyses were taken from the same branches. The assessments were performed during August 1992, and were repeated in January 1993. Two-year-old branchlets (1990) were cut off with clean scissors. Needle samples having a fresh weight of about 3 g were immediately placed in screw-cap glass vials (7 X 2.5 cm), which had been kept in a drying oven at 120°C for over 12 h. Just before the field trip, they were removed from the oven and the caps were tightly closed. The samples were sent to Tiibingen by air mail, arriving within 2-3 days. TCA analyses were performed as follows. A portion of about 1.5 g of the needles was accurately weighed, rinsed with distilled water, and homogenized in liquid nitrogen in a porcelain mortar. Distilled water (6 ml) was added to the homogenate, and after ultrasonification, the tissue debris was sedimented by centrifugation. An aliquot (4 ml) of the clear supematant was mixed with dichloroacetic acid (330 ng) as internal standard and acidified with 10 drops of concentrated sulfur acid to pH 1. TCA was extracted with 1.5 ml diethyl ether, derivatized to the methyl ester with diazomethane, and analyzed by capillary gas chromatography and electron-capture detection (Carlo Erba Strumentazione, Milan). Recovery of TCA extraction and derivatization have been determined as 93 f 9% (Frank et al., 1990). Calibrations were performed once a month by spiking

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aliquots of homogenate of conifer needles with freshly prepared aqueous solutions of 5-200 ng TCA in 100 ~1 distilled water. 3. Results The average needle loss (NL) was 45% (range 25-90%) (Table 1). The average trichloroacetic acid concentration in needles was 33 rig/g (range 8-65 rig/g). The trees could be divided into two groups on the basis of the TCA content in the needles and the degree of defoliation (Fig. 1). In group 1, needle loss was < 45%, and it increased less steeply when the TCA concentration increased. In group 2, needle loss exceeded 45% at low TCA concentrations, and it increased more steeply when the concentration increased. The latter correlation was 0.76 (P = 0.003) and the former was slightly less at 0.74 (P = 0.005). The first of the two might be called TCA-resistant and the second TCA-sensitive. The difference between the sensitivity groups also became evident in the length of branch covered by needles (LBT). This value was shorter in the TCA-sensitive group than in the resistant group (Table 1). The difference was not significant because of a relatively wide variation. LBT decreased as the TCA concentration increased in both groups (Fig. 2). The correlation coefficients were ri = -0.49 and r2 = -0.54.

TCA(ngg-1) +

Group

-c--

Group2

1

y = 1 lxW.31

r = 0.74

p=o.o05

y = 26xW.26

r = 0.76

p=0.003

Fig. 1. Relationship between TCA content in pine needles (August 1992) and needle loss in TCA-resistant group 1 and TCA-sensitive group 2.

The mean length of current annual shoots on a first-order branch (LCS) was also shorter in the TCA-sensitive group than in the resistant group (Table 1) but again the difference was not significant. LCS decreased with increasing TCA concentration in both groups (Fig. 3). The correlation coefficients were nearly equal (yl = -0.31 and r2 = -0.36). Shortening may be a consequence mainly of decreased photosynthetic needle mass. Both the total number of needle age classes in August (NNT) and the number of needle age

Table 1 Characteristics of experimental trees by sensitivity group (mean and range) Groupa

N

TCA w/g

NL%

LBT mm

LBY mm

LCS mm

NNTn

NNY n

NPB II

NNA n

1

11

2

9

39 16-65 25 8-54 33 8-65

34 25-45 58 45-90 45 25-90

124 72-220 101 60-140 114 60-220

21 o-75 12 O-30 17 o-75

27 15-35 23 17-32 25 15-35

5.5 5-7 5.1 4-7 5.4 4-7

1.0 o-2 0.7 o-2 0.9 o-2

1.3 o-3 2.2 o-4 1.7 o-4

4.5 3-5 4.4 3-6 4.5 3-6

Total

20

N, number of trees; TCA, concentration of trichloroacetic acid; NL, premature needle loss, percent; LBT, total length of branch part with needles in August 1992 (mm); LBY, length of branch part with yellow needles falling off in the same autumn (mm); LCS, length of current annual shoot on a first-order branch (mm); NNT, total number of needle age classes in August 1992; NNY, number of needle age classes yellowing and falling off in the same autumn; NPB, number of pulvinated branchlets, i.e. annual shoots with needle scars left indicating number of needle age classes fallen off recently (during about 1 year); NNA, number of needle age classes attached in the following winter (January 1993). ‘Group 1, TCA-resistant; Group 2, TCA-sensitive.

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b 60

v. 0

20

40

60

SO

4

Group

-a-

Group2

1

y = 183 - 1.64x

r = -0.49

y=130-1.18x

r=-O.54

Number

Fig. 2. Relationship between TCA content in pine needles and the total length of branch part with needles in August in TCA-resistant group 1 and TCA-sensitive group 2.

classes attached in the following winter (NNA) had a negative correlation with TCA concentration (P < 0.10). When the latter decreased, the number of needle age classes increased in both groups (Fig. 4). Only the difference between the groups for four NNA classes was slight. The aver-

d0

20

40

60

I

Group

-E--

Group2

1

y=32-0.1x

r = -0.31

~126-0.1~

r = -0.36

3

4

5-6

J

NNA of needle age classes

Fig. 4. Average TCA content in pine needles by total number of needle age classes (NNT) and number of needle age classes attached in the winter (NNA) for the TCA-resistant group 1 and TCA-sensitive group 2.

age TCA concentration of the sensitive group had significant differences in the needle age classes (Fig. 4). The total number of needle age classes in August was larger in the resistant group (mean = 5.5, range = 5-7) than in the sensitive group (mean = 5.1, range = 4-7). During the winter, this difference almost disappeared (means = 4.5 and 4.4; Table 1). The sensitive group, however, had lost one more needle age class, on an average, than the resistant group. More than half of the trees in the former group had shed 3-4 needle age classes during the past year (i.e. NPB = 3-4). These trees now shed no needles at all (NNY = 0). There was one exception: one tree had shed four needle age classes and dropped yet another needle age class. NPB was two or less in the resistant group. 4. Discussion

60

TCA ( ng g -1) 6

6-7 NNT

TCA ( ng g -1) +

5

Fig. 3. Relationship between TCA content in pine needles and the length of current annual shoot on a first-order branch (LCS) in TCA-resistant group 1 and TCA-sensitive group 2.

The results reveal a correlation between the degree of defoliation and the TCA content of needles, as found earlier (Frank et al., 1992a,b, 1994). Two groups of individual trees with different sensitivities to TCA concentration can be discerned. At present, only speculative attempts

Y Norokopi, H. Frank / Sci. Total Entiron. 160 / I61 (1995) 459-463

to explain the differences are possible. It most likely depends on the physiological defense potency of trees against airborne TCA or a faster elimination of the xenobiotic. These two groups serve as a basis for further studies on morphological, anatomical, and biochemical parameters. Needle loss is a nonspecific phenomenon. Therefore, it may not be a particularly good indicator of the effects of TCA accompanied by many variable factors. The degree of defoliation shows, however, the general vitality of trees. TCA is only one of several phytotoxic air pollutants that may be involved in the induction of tree damage. Suspect compounds are other haloacetic acids and their derivatives, nitrophenols, and pentachlorophenol (Frank et al., 1992b, 1994). TCA is an indicator for the distribution and deposition of phytotoxic photooxidants, derived from the anthropogenic C,-chlorocarbons ubiquitously occurring in the atmosphere of the northern hemisphere (Fabian, 1986). References Aberg, B., 1992. Plant growth regulators. Swed. J. Agric. Res., 12: 51-61. Barrons, K.C. and R.W. Hummer, 1951. Basic herbicidal studies with derivatives of TCA. Agric. Chem., 6: 48-121. Fabian, P., 1986. Halogenated hydrocarbons in the atrnosphere. In: 0. Hutzinger (Ed.), The Handbook of Environmental Chemistry, Vol. 4A. Springer-Verlag, Berlin, pp, 23-51.

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Frank, H., 1991. Airborne chlorocarbons, photooxidants and forest decline. Ambio, 20: 13-18. Frank, H. and W. Frank, 1985. Chlorophyll bleaching by atmospheric pollutants and sunlight. Naturwissenschaften, 72: 139-141. Frank, H., A. Vmcon, J. Reiss and H. Scholl, 1990. Trichloroacetic acid in the foliage of forest trees. J. High Resol. Chromatogr., 13: 733-736. Frank, H., H. Scholl, S. Sutinen and Y. Norokorpi, 1992a. Trichloroacetic acid, a ubiquitous herbicide in Finnish forest trees. In: E. Tikkanen, M. Varmola and T. Katermaa (Eds.), Symposium on the State of the Environment and Environmental Monitoring in Northern Fennoscandia and the Kola Peninsula, 6-8 October 1992, Rovaniemi, Finland, Extended Abstracts. Arctic Centre Publications, 4: 259-261. Frank, H., H. Scholl, S. Sutinen and Y. Norokorpi, 1992b. Trichloroacetic acid in conifer needles in Finland. Arm. Bot. Fenn., 29: 263-267. Frank, H., H. Scholl, D. Renschen, B. Rether, A. Laouedj and Y. Norokorpi, 1994. Haloacetic acids, phytotoxic secondary air pollutants, Environ. Sci. Pollut. Res., l(1): 4-14. Jukola-Sulonen, E.-L., K. Mikkola and M. Salemaa, 1990. The vitality of conifers in Finland. In: P. Kauppi, P. Anttila and K. Kenttamies (Eds.), Acidification in Finland. SpringerVerlag, Berlin, pp. 523-560. Juuti, S., A. Hirvonen, J. Tarhanen, J.K. Holopainen and J. Ruuskanen, 1993. Trichloroacetic acid in pine needles in the vicinity of a pulp mill. Chemosphere, 26: 1859-1868. Norokorpi, Y. and H. Frank, 1993. Effect of stand density on damage to birch (Bemla pubescens) caused by phytotoxic air pollutants. Ann. Bot. Fenn., 30: 181-187. Pliimacher, J. and I. Renner, 1992. Volatile chlorinated hydrocarbons and trichloroacetic acids in conifer needles. The 2nd IMTOX-workshop, lo-11 December 1992, GarmishPartenkirchen.