The product from the burning of a combination of carbonaceous materials.

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

Not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP compliant, non-guideline experimental study. Study published in a scientific, peer reviewed journal.

Qualifier:

no guideline available

Principles of method if other than guideline:

Toxicity of leachate from bottom ash used in road construction was studied with a mung bean (Phaseolus aureus) assay in a three year follow-up study. Leachates were collected with lysimeters on the field. From the leachates, elemental composition, pH, TOC, TS, conductivity, and ions were analysed prior the toxicity test. In the toxicity test performed in laboratory, root and shoot elongation was studied.

GLP compliance:

no

Details on sampling:

Leachates were collected with lysimeters between October 2001 and October 2004. Lysimeters were sampled 21 times. Dimensions of the lysimeters were 2 m x 15 m and they contained 26 t of bottom ash or gravel. Lysimeters were placed partly under the body of the road and partly under the slope of the road.
Samples were stored frozen before analysis and test unfiltered except for samples collected in autumn 2001 which were filtered with Munkell filter V120H.

Species:

Phaseolus aureus

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Mung bean
- Plant family: Fabaceae
- Source of seed: Risenta AB, Sweden
- Prior seed treatment/sterilization: Rinsed with tap water and soaked overnight in distilled water. After this, beans were rinsed three times with distilled water.

Test type:

seed germination/root elongation toxicity test

Study type:

laboratory study

Substrate type:

filter paper

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

None

Test temperature:

25°C

pH:

9.5-11.6

Moisture:

No data

Details on test conditions:

- 20 mung beans on Whatman No. 1 filter papers in Petri dishes with a diameter of 100 mm
- Amount of leachate: 8 ml per dish
- Incubation: in darkness at 25°C
- After 72 hours, beans were rinsed five times with distilled water and coats were removed

Nominal and measured concentrations:

Measured concentrations of the leakage: Al (34.2-39.2 mg/L), Cl (2914-16446 mg/L), Cu (0.48-1.92 mg/L), K (197-847 mg/L), Na (766-4180 mg/L), NH4-N (1.80-8.47 mg/L), tot-N (12.0-18.5 mg/L) and TOC (34.0-99.0 mg/L).

Reference substance (positive control):

no

Species:

other: mung bean

Remarks on result:

other: Effect concentrations were not determined

Details on results:

Compared to gravel, the first bottom ash leachate sampled reduced root elognation with 73 ± 15% (α = 0.001, p < 0.001 ANOVA) (See Fig.). The amount of chlorine was found to have significant effect on the reduction of root elognation (See Fig.).

Reported statistics and error estimates:

Leachate quality samples one and two were found to be positioned outside of the 95% confidence ellipse. The thawling water was not found to affect the leachate quality (α = 0.05).

Ash leachate had ad adverse effect on mung bean roots. Effect concentrations were not, however, reported in the study.

Validity criteria fulfilled:

not specified

Conclusions:

Leaching of hazardous substances from the road constructed with bottom ash produced by burning municipal solid waste causing toxic effects in mung bean was greatest close to the construction time. The critical components identified during the first year were Cl, Cu, K, Na, NH4-N and TOC. In three years, leaching of Al, Cr and NO2 -N increased. Ca, Co, Fe, Mn, Ni, No3-N and Pb were not found to leach during the study.

Executive summary:

Toxicity of leachate from bottom ash used in road construction was studied in a non-GLP and non-guideline compliant investigation with a mung bean (Phaseolus aureus) as a test organism. Leachate from gravel was used in comparison. Leachates were collected with lysimeters during the 36 month follow-up time. From the leachates, elemental composition, pH, TOC, TS, conductivity, and ions were analysed prior the toxicity test. In the test, root and shoot elongation was studied. The mung beans were rinsed with tap water and soaked overnight in distilled water. The beans were incubated on Whatman filters in Petri dishes in darkness at 25°C for 72h followed by rinsing and removal of coats of beans.

 

The study showed, that the initial leachate reduced the root length 73 ± 15% (p < 0.001). The toxic effect was found to correlate with the amount of chlorine in the leachate. The high salinity was concluded to possibly mask the inhibitory effect of e.g. Al, Cu, TOC and nitrate compounds. Additionally, TOC was reported to have tendency to form metal complexes, which may decrease toxic effects. The critical components identified during the first year were Cl, Cu, K, Na, NH₄-N and TOC. Concentrations of the leaching components were observed to reach the level of gravel road during the three years study period except for concentrations of Al, Cr and NO₂ -N, which were found to increase. Conductivity decreased to the level of gravel in one year. Ca, Co, Fe, Mn, Ni, No₃-N and Pb were not found to leach during the study. It is well known, that the test organism mung bean is unable to tolerate salinity.

Reference 2

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1996 - 1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: A non-GLP compliant, non-Guideline field study

Qualifier:

no guideline available

Principles of method if other than guideline:

Field experiments were established in order to study effects of wood ash on vegetation. The ash induced changes in forest vegetation were studied using the amount of species and sampling fraction in the bottom and field layers.

GLP compliance:

no

Test type:

other: concentration of metals

Study type:

field study

Substrate type:

natural soil

Species:

other: Several species

Remarks on result:

not measured/tested

Remarks:

The components that were analysed from ashes and plant material were Al, As, B, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, S, Ti, V and Zn.

Depending on the amount of ash in application, the potassium concentration in lingonberries was 7,1 - 8,0 mg/g, compared to 5,5 mg/g in those plots, where ash application was not done. Titanium concentrations varied between 0,5 - 0,8 mg/kg, arsenic concentrations between 1,0 - 1,1 mg/kg and chromium concentrations between 0,2 - 0,5 mg/kg in the berries of one experimental plot.

Conclusions:

The effects of ash could be seen already on the year of application. The changes in elemental concentrations of berries reflected the elemental concentrations of different kinds of ashes and the doses used.
Generally, ash was seen to induce elevation of phosphorous, potassium and borium concentrations in berries. The concentrations of calsium, aluminium and manganese were variable. During two first years of application concentrations of titanium, arsenic, chromium and sometimes also sulphur in berries were temporarily elevated. There was no change or a slight decrease in the concentration of copper, zinc and cadmium.
On a long run, concentrations of cadmium, sometimes even of copper and zinc, were reduced in berries. The reason for this decrease could be the ash induced raise in pH and consequently decrease in a leachable fraction of metals.

Executive summary:

A non-GLP, non guideline field study was established in order to study effects of wood ash on vegetation. From experimental plots, plant material was gathered after ash application.

Concentrations of phosphorous, calcium and boron in berries increased during the summer after the ash treatment. Large ash doses also increased the concentrations of some heavy metals (chromium, titan, arsenic) in berries. Concentrations of cadmium in berries were unaltered or decreased. In the previous ash treatment tests, the trace element concentrations in berries were in the same level despite of the treatment. Cadmium concentration in cloudberries decreased in the ash treated areas in the long run.

Concentration of phosphorous, potassium, calcium and boron were elevated in mushrooms in the short run. In some cases, concentrations of aluminium, arsenic, and chromium in mushrooms increased. Also, concentration of ferric was elevated in mushrooms from the areas treated with peat ash. In cadmium concentrations, evident changes were not observed. In a peat land experiment, the abundance of inrolled paxil increased significantly within a year after the ash treatment. Changes in nutritional element composition in mushroom could be detected for many years, even for 10-20 years, after the ash treatment. Concentrations of cadmium were unaltered or increased slightly in the long run.

Concentrations of calcium, boron, potassium and phosphorous in pine needles were elevated during the year and the half followed by the ash treatment. The impact was more evident in the peat lands than in the moore areas. In the needle analysis, the improvement in nutritional conditions was found to be long-lasting.

Reference 3

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1993-2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: A non-GLP compliant , non-Guideline field study

Qualifier:

no guideline available

Principles of method if other than guideline:

Metal concentrations in different parts of vegetation established in ash material was determined and compared to concentrations in vegetation grown in a reference material.

GLP compliance:

no

Remarks:

A WOE field study

Species:

other: Salix, Betula

Test type:

other: accumulation of metals in vegetation

Study type:

semi-field study

Substrate type:

other: Ash

Species:

other: Betula Salix

Dose descriptor:

other: elemental concentrations in different plant parts

Nominal / measured:

not specified

Remarks on result:

not measured/tested

Translocation factors (leaves : leachable concentration; Betula sp.)

	Crushed stone	Wood ash
As	23± 11 a	6 ± 3 a
Cd	899 ± 896 a	79 ± 84 a
Cr	64 ± 7 a	12± 4 b
Cu	32 ± 17 a	62 ± 54 a
Ni	49 ± 8 a	47 ± 44 a
Pb	75 ± 55 a	11 ± 14 a
Sb	6075 ± 2264 a	896 ± 569 b
Zn	36 ± 13 a	2 ± 1 b

The different alphabets (a/b) for a substance on a same row indicate a signicant difference (P<0,05) in translocation factors.

Conclusions:

The higher total metal content in wood ash compared to in crushed stone was not reflected in the accumulation of metals in the vegetation.

Executive summary:

A non-GLP, non-guideline compliant experiment was established to study accumulation of metals in vegetation. Ash material was taken from a 15 -year-old lysimeter. Although the total metal content in ash was much higher than in crushed stone, this was not reflected in the accumulation of metals in the vegetation. With the exception of As and Sb, no, or only small, differences in metal content in grazable parts of birch and Salix trees grown in wood ash and trees grown in crushed stone were observed.

The translocation factors (i.e. the quota between concentration in leaves and total concentration in the wood ash and crushed stone) for Cr, Cu, Ni, Pb, Sb and Zn were higher in the trees that had grown in crushed stone than in those grown in wood ash. The mobility of Cd, Cr, Cu, Ni, Sb and Zn, estimated as leachability (the quota between leachable concentration and total concentration) was lower in the studied ash than in the crushed stone. The leachability of As was higher in ash than in the crushed stone.

Reference 4

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1995-2000

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: A non-GLP compliant, non-Guideline experimental study. Study published in a scientific, peer reviewed journal.

Qualifier:

no guideline available

Principles of method if other than guideline:

The impact of different doses and two types of wood ash on ground flora was studied over a 5-year period following ash application to a medium-aged Scots pine stand.

GLP compliance:

no

Plant group:

Bryophyta or Hepatophyta (mosses or liverworths)

Details on test organisms:

Bryophytes found in the test area included: Pleurozium schreberi, Dicranum majus, Dicranum polysetu, Dicranum scoparium, Dicranum spuriu, Dicranum montanum, Pohlia nutans, Mnium spp., Plagiothecium curvifolium.

Plant group:

other: Lichens

Details on test organisms:

Lichens found in the test area included Cladina arbuscula, Cladina rangiferina, Cladina stellaris, Cetraria islandica, Cladonia spp

Plant group:

other: vascular plants

Details on test organisms:

Vascular plants found in the test area included Betula sp., Picea abies, Pinus sylvestris, Vaccinium myrtillus, Vaccinium vitis-idaea, Calluna vulgaris,
Deschampsia flexuosa, Empetrum nigrum, Melampyrum spp., Convallaria majalis, Lycopodium complanatum.

Test type:

other: vegetation composition and damage

Study type:

field study

Substrate type:

natural soil

Total exposure duration:

60 mo

Test temperature:

The annual mean temperature 3.9 °C

pH:

Soil pH was 4.0

Moisture:

The annual mean precipitation is 730 mm.

Details on test conditions:

The experiment was conducted in a 50-year old Scots pine (Pinus sylvestris L.) stand, situated in the northern part of the county of Västmanland, in the central part of Sweden (59° 4'N, 15° 32'E, altitude 135 m a.s.l.). The annual mean precipitation is 730 mm, and the annual mean temperature 3.9 °C. The soil is characterized as a thick, mesic, sandy sediment, with a clearly eluviated horizon. The mor layer averaged a depth of c. 4 cm and had a pH (H2O) of 4.0. The ground flora was dominated by Vaccinium myrtillus L., interspersed with Vaccinium vitis-idaea L. and some Calluna vulgaris L. The bottom layer was dominated by Pleurozium schreberi (Brid.) Mitt., Dicranum polysetum Sw. and reindeer lichens (Cladina spp.).
The whole experiment comprised ten treatments, each with three replicates, arranged in blocks. Study plots were 30 x 30 m in size. The ground flora was surveyed in seven of the treatments. These were: the control; self-hardened, crushed wood ash applied at a rate of 3, 6 and 9 tons ha–1; nitrogen applied at a rate of 150 kg ha–1; a combined treatment of 150 kg N and 3 tons of crushed wood ash per hectare; and pelleted wood ash applied at 3 tons ha-1. Nitrogen was applied in the form of ammonium nitrate with lime (N 27.5%, Ca 4.0%, Mg 1.0% and B 0.2%). Twelve permanent quadrats (0.5 ´ 0.5 m) were placed at regular intervals within each study plot. The cover of each individual species was estimated by eye, as if projected onto the ground, to the nearest one per cent. Ten vascular plant species and one collective genera (Melampyrum spp.), nine bryophyte species and one collective genera (Mnium spp.), and four lichen species and one collective genera (Cladonia spp.) were recorded at the initiation of the study.The degree of damage to the bryophytes and lichens was estimated according to the following scale: 1) undamaged – healthy shoots; 2) brown discolouration; 3) dark brown or black and quite dry – seemingly dead. The percentage cover of each damage category was recorded in each quadrat. The vegetation was surveyed in 1995, before the treatments were applied, and subsequently in 1996, 1997 and 2000. During the last two weeks in June in each of these years, the same surveyor examined the quadrats. Species mean cover, as well as the degree of damage to the bryophytes and lichens, was calculated for each plot and treatment (i.e. the arithmetic mean of the 12 quadrats), for use in the subsequent analyses.

Nominal and measured concentrations:

Crushed ash
Macroelements (g/kg dw)
Ca: 137, Mg: 14, K: 64, P: 8, Al: 19, Mn: 8, S: 5, C: 2, Si: 56
Trace elements (mg/kg dw)
As: 9, Pb: 108, Cd: 12, Cu: 108, Cr: 56, Ni: 114, Zn: 3360, V: 77, Hg: 0.28

Pelleted ash
Macroelements (g/kg dw)
Ca: 152, Mg: 14, K: 35, P: 8, Al: 31, Mn: 1, S: 3, C: 216, Si: 94
Trace elements (mg/kg)
As: 15, Pb: 70, Cd: 9, Cu: 104, Cr: 54, Ni: 39, Zn: 3990, V: 37, Hg: 0.87

Species:

other: Several

Duration:

60 mo

Remarks on result:

not measured/tested

Remarks:

The endpoints determined included vegetation composition and “burning” damage (discoloration) to the bryophytes. No EC-, ER-, LC-, NOEC or LOEC-values were measured.

Details on results:

For all treatments combined, there was no change in the presence of species during the survey period, i.e. there were no local extinctions or colonizations. Only minor changes in the relative amount of species occurred in the treatments. There was a range, although small, from mesic, fertile conditions to rather dry and somewhat less fertile ones. The magnitude of changes between years for the different treatments were rather similar and were not more pronounced than those for the untreated control plots. Further, there were both positive and negative trends in many of the treatments, indicating small and inconsistent fluctuations. The three most frequently occurring bryophytes, D. polysetum, H. splendens and P. schreberi, had clearly suffered severe visible damage after treatment with crushed ash, even at the lowest dose. The damage to the bryophytes was greatest in the first year after treatment. In the second year following treatment, new bryophyte shoots had started to appear. After five years, there was no visible damage, since the dead bryophyte shoots were either classified as litter or were covered by new shoots and needle litter. The species most susceptible to damage by the crushed ash application was D. polysetum, for which, even at the lowest dose (3 tons ha–1), 90% of the cover was recorded as damaged or dead after one year.

The addition of wood ash, including pelleted ash, led to significant reductions in cover of the Cladina species. These reductions were also significant when the impact of the increased cover of litter was excluded. The treatments also affected the field layer species. All wood ash treatments tended to lead to a decrease in the cover of dwarf shrubs. The difference was significant for V. vitis-idaea with 9 tons ha-1 of crushed ash and for Calluna vulgaris (L.) Hull with 6 tons ha-1 of crushed ash. The presence of Melampyrum spp., although with very low cover values, increased on the crushed ash treated plots. Nitrogen addition tended to lead to an increase in the cover of V. myrtillus and a decrease in the cover of V. vitisidaea and C. vulgaris. The trends for vegetation cover over time for the different ash treatments were most obvious, and highly significant, for the Cladina lichens. The trends were not so clear for the bryophytes. However, there were significant treatment effects for the higher doses of crushed ash on D. polysetum and P. schreberi.

Reported statistics and error estimates:

- The percentage variance explained in the PCA was 29.9 and the eigenvalue for the first axis was 3.59. Only minor changes in the relative amount of species occurred in the treatments. The only clear trend was for the treatment with nitrogen and ash, in which the vegetation of all three replicates moved towards the more fertile Vaccinium–Hylocomium community.
- The trends for vegetation cover over time for the different ash treatments were most obvious, and highly significant (p < 0.05), for the Cladina lichen.
- The effect of the combined treatment of N and crushed wood ash was not significantly different from the effect of crushed wood ash alone. No significant effects were found following treatment with pelleted ash or N treatment alone.
- Increase in amount of litter during 5-yr study period was directly proportional to a decrease in the total cover of the bottom layer species, and statistically significant (p < 0.05) in the plot treated with 9 tons ha–1 of crushed ash and in the two N treated plots. The N treatment also significantly (p < 0.05) reduced bryophyte cover, mainly through a decrease in the cover of Pleurozium schreberi.
- The addition of wood ash, including pelleted ash, led to significant reductions (p < 0.05) in cover of the Cladina species. These reductions were also significant when the impact of the increased cover of litter was excluded.
- All wood ash treatments tended to lead to a decrease in the cover of dwarf shrubs. The difference was significant for V. vitis-idaea with 9 tons ha-1 of crushed ash and for Calluna vulgaris (L.) Hull with 6 tons ha-1 of crushed ash.
- The trends for vegetation cover over time for the different ash treatments were most obvious, and highly significant, for the Cladina lichens. There were significant treatment effects for the higher doses of crushed ash on D. polysetum and P. schreberi. Significant effects were also found for the N treatment on P. schreberi and Cladina arbuscula+C. rangiferina.

The endpoints determined included vegetation composition and “burning” damage (discoloration) to the

bryophytes. No EC-, ER-, LC-, NOEC or LOEC-values were measured.

Conclusions:

The most obvious effect in this study was the initial “burning” damage (discoloration) to the bryophytes in plots treated with the rapidly soluble, crushed wood ash. The changes in the overall vegetation composition after thewood ash treatments were small. Acidophilous dwarf shrubs
were negatively affected by the wood ash additions. The addition of wood ash, in a soluble form and/or containing fine particle fractions, may cause changes in the ground vegetation, either by direct chemical damage, or indirectly by changing the soil chemistry. The vegetation will recover though, and after five years the species composition was unalterd from what it was prior ash application.

Executive summary:

The impact of different doses and types of wood ash on ground flora was studied with a non GLP non guideline field study over a 5 -year period following ash application to a medium-aged Scots pine stand in the central part of Sweden. Generally, there were only minor changes in the vegetation cover as a result of the treatments, and the species composition was unaltered after five years. When treated with hardened and crushed wood ash, the three most common bryophytes reacted rapidly, displaying severe visible damage in the initial phase of the study period. Two years after ash application, the bryophytes had started to recover, and after five years no visible damage could be discerned. At the highest ash dose (9 tons ha-1), however, the cover of bryophytes was significantly reduced, even after five years. No visible damage to the bryophytes was found after treatment with pelleted ash or after N treatment, and no visible damage to lichens was found for any treatment. However, by the end of the study period, the addition of wood ash, including the pelleted ash, had significantly reduced the cover of Cladina lichens. All wood ash treatments tended to lead to a decrease in the cover of dwarf shrubs.

Reference 5

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Principles of method if other than guideline:

Forest fertilization study using mixed wood ash. Trace metal (Cd, Cr, Cu, Mn, Ni, Pb, Zn) concentrations were monitored throughout the 3 years in
different components of the forest ecosystem—soil solid fraction, soil solution, tree needles, ground vegetation and different
mushroom species.

GLP compliance:

no

Species:

other: Pinus radiata

Plant group:

other: Pinaceae

Species:

other: Amanita muscaria (L.: Fr) Hooker

Plant group:

other: Fungi

Species:

other: Russula sardonia Fr. em. Rom. NC

Plant group:

other: fungi

Species:

other: Tricholoma pessundatum (Fr.) Quel. Denmark

Plant group:

other: Fungi

Species:

other: Laccaria laccata (Scop.:Fr) Berk. and Broome

Plant group:

other: Fungi

Species:

other: Suillus bovinus (L.: Fr.) Kuntze

Plant group:

other: Fungi

Species:

other: Micena pura Pers. Ex Fr. Krummer

Plant group:

other: Fungi

Species:

other: Xerocomus badius (Fr.) Kuhn.: Gilb

Plant group:

other: Fungi

Species:

other: Pseudarrenatherum longifolium

Plant group:

other: Poaceae

Study type:

field study

Substrate type:

natural soil

Total exposure duration:

36 mo

Test temperature:

Ambient

Details on test conditions:

The study was carried out in six radiata pine (P. radiata) plantations located in northwestern Spain, in the provinces of Lugo and A Coruña. The age of the plantations ranged from 2 to 19 years. The stands were situated at altitudes of between 470 and 500 m (measured from mean sea level). The climate of the area is classified as temperate subtropical with humid winter. The average annual precipitation is 1200–1800 mm and the average minimum and maximum temperatures of 3–4 °C and 22–24 °C, occur in January and July, respectively.

Species:

other: Several species

Remarks on result:

not measured/tested

Remarks:

Trace metal (Cd, Cr, Cu, Mn, Ni, Pb, Zn) concentrations were monitored throughout the 3 years in different components of the forest ecosystem

Reported statistics and error estimates:

The effects of wood ash application on heavy metal concentration in soil and vegetation were examined by analyses of variance. Data were assessed for homogeneity and normality. Changes over time were tested by analysis of repeated measurements. When this test revealed significant differences for the whole period, the mean monthly values were compared by Tukey's means test. Differences were considered significant at p<0.05 for all parameters. The relationships among the concentrations of trace elements in soil and plants were analyzed by Pearson's correlation and stepwise linear analyses.

Repeated fertilization application of wood ash caused local effects to soil. Soil pH increased slightly in upper layer soil after the second application of ash, both in soil solution and extractable fraction. The single application of mixed wood ash had no effect on pH in the uppermost soil layer. The concentrations of Mn, Ni and Cr in the extractable fraction of the soil and soil solution were related to the total contents in the soil (r=0.40–0.63; p<0.05). Again, increase in the soil concentrations of soluble and extractable Mn and Zn was detected after the third application of ash.

 

The concentrations of Mn, Ni, Cu and Cr in tree foliage were significantly related to the respective total and extractable metal concentrations in soil (r=0.4–0.6; p<0.05). There was also a negative relationship between the concentration of Cu in needles and soil pH. Wood ash application had little effect on the concentrations of trace elements in tree foliage, in October 2005, two and a half years after application. The only effect was a slight decrease in foliar Mn after the third application at site 6.

 

Fertilization did not affect ground vegetation (vascular plants).

 

The bioconcentration factor (BCF) was below 1 for Mn, Ni and Pb. Instead, all of the mushroom species bioaccumulated Zn, Cu and Cd. The highest concentrations were observed in X. badius and A. muscaria. Wood ash application led to increased Mn levels in most of the mushrooms at both sites. The greatest increases occurred in M. pura, L. laccata and Tricholoma pessuxdatum. The latter species began accumulating Mn after the first application The initial concentrations of Zn in mushrooms ranged between 10 and 250 mg kg−1, with maximum accumulation occurring in X. badius and A. muscaria. The clearest effect of the treatments was the decrease in the concentration of Zn in X. badius. The concentrations of Zn in other mushroom species were either not affected or decreased slightly. The range of concentrations of Cu and Cd in the different mushroom species was 2–110 mg kg−1 and 1–6 mg kg−1, respectively. Changes attributable to the treatment with ash only occurred in X. badius, in which the concentrations of these elements decreased significantly after application of wood ash. The levels of Ni, Cr and Pb were not affected by the treatments.

Conclusions:

The single application of mixed wood ash in forest fertilization did not have effect on pH in the uppermost soil layer. Instead, repeated fertilization caused slight increase in pH in the uppermost soil layer. Application of mixed wood ash (fly and bottom wood ash) to forest soils did not cause
increased availability of trace elements in the short or medium term (1–3 years), even with multiple applications of the ash. The only exception to this was the pattern observed for Mn, as the concentration of this element increased in soils and mushrooms after application of the ash to the soil. Fertilization did not cause any effects of vascular plants.

Executive summary:

In a three-year field study, mixed wood ash (fly and bottom wood ash) was used in forest (P. radiata) plantation fertilization. The used ash was mainly derived from the combustion of bark (85–90% Pinus spp. and 10–15% Eucalyptus spp.). The study included two types of experiments: a single fertilization and multiple fertilizations, both with control plots. The annual dosing of wood ash was 4500 kg ha-1. Both pH and trace metal (Cd, Cr, Cu, Mn, Ni, Pb, Zn) concentrations were monitored in different components of the forest ecosystem: soil solid fraction, soil solution, tree needles, ground vegetation and different mushroom species. The repeated fertilization caused slight increase in pH and increase of Mn and Zn concentrations in the uppermost soil layer. The maximum concentrations of trace metals did not reach levels potentially harmful to organisms. Wood ash application led to increased Mn levels in most of the mushrooms at both sites. The greatest increases occurred in M. pura, L. laccata and Tricholoma pessuxdatum. The latter species began accumulating Mn after the first application. However, the bioconcentration factor (BCF) was below 1 for Mn, Ni and Pb. Instead, all the mushroom species bioaccumulated Zn, Cu and Cd (BCF≥1), with the highest concentrations observed in X. badius and A. muscaria. Concentrations of Zn, Cu and Cd decreased in some mushroom species, probably because of increased soil pH caused by the fertilization treatment. Heavy metal concentrations in tree needles and ground vegetation were not altered.

Description of key information

Toxicity of ash on terrestrial plants was estimated based on four scientific publications from literature. In the first investigation, toxicity of leachates from bottom ash used in road construction to mung bean was studied. In the second investigation, bioaccumulation of ash-originated elements in trees was studied. In the last three investigations, long-term (up to 5 years) effects of ash amendments on vegetation were studied in field, including one study of the medium term monitoring (1-3 years) of trace elements after the mixed wood ash addition in the field. Leachates from bottom ash used in road construction were found to be toxic to mung bean but toxicity was correlated with concentration of chlorine in leachate. Trees grown on ash-containing material were not found to bioaccumulate ash-derived metals. Instead, concentrations of As and Cr in berries were temporarily elevated during the two first years of ash-application. On a long run, however, concentrations of Cd, Zn and Cu were reduced in berries. Impacts of ash amendments on ground flora in field were subtle. The most obvious effect was the initial discolouration of bryophytes. Mixed wood ash did not have an influence on increased availability of trace metals from soils even after three year monitoring time. However, some mushroom species tend to have an increase of Mn after the wood ash was added repeatedly. This did not reach the harmful level to organisms.  

Additional information

Ash is at the same time a source of nutrient elements and of lime. Its application to soil causes increases in the soil pH and the contents of most major nutrient elements and in most cases decreases the availability of Al and minor elements. The benefits on the growth of plants are the result of an increase in available P, Ca, Mg, K and B and a decrease in Al and Mn toxicity. Organic carbon has a tendency to form metal complexes, which may decrease toxic effects for plants.

 

Ash may induce burning damages in sensitive species like bryophytes. Both high pH and high concentration of neutral salts can cause damage to bryophytes and lichens. The damage is usually not irreversible. Toxic effects from leachate from ash have been reported for species that is known to be sensitive to high salinity. High salinity may possibly mask the inhibitory effect of e.g. Al, Cu, TOC and nitrate compounds. Even though the mixed ash addition was repeated many times between three years, there was not altered heavy metal concentrations observed in tree needles or ground vegetation. Only mushrooms contained increased levels of Mn.