Arsenic Accumulation and Speciation in Macrophytes - ACS Publications

Jul 14, 2016 - ... Building, Alexander Crum Brown Road, Edinburgh EH9 3FF, Scotland, ... and entering the Danube River.2 The Hungarian red mud spill...
0 downloads 0 Views 776KB Size
Subscriber access provided by UNIV OF NEW ENGLAND

Article

Assessing the legacy of red mud pollution in a shallow freshwater lake: arsenic accumulation and speciation in macrophytes Justyna P. Olszewska, Andrew A. Meharg, Katherine Victoria Heal, Manus Patrick Carey, Iain D. M. Gunn, Kate R. Searle, Ian J. Winfield, and Bryan M. Spears Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00942 • Publication Date (Web): 14 Jul 2016 Downloaded from http://pubs.acs.org on July 26, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29

Environmental Science & Technology

1

Assessing the legacy of red mud pollution in a shallow freshwater lake: arsenic

2

accumulation and speciation in macrophytes

3 4

Justyna P. Olszewska,1,2 Andrew A. Meharg,3 Kate V. Heal,2 Manus Carey,3 Iain D. M.

5

Gunn,1 Kate R. Searle,1 Ian J. Winfield,4 and Bryan M. Spears*,1

6

1. Centre for Ecology & Hydrology (CEH Edinburgh), Bush Estate, Penicuik EH26 0QB,

7

Scotland, UK

8

2. School of GeoSciences, The University of Edinburgh, Crew Building, Alexander Crum

9

Brown Road, Edinburgh EH9 3FF, Scotland, UK

10

3. Institute for Global Food Security, Queen’s University Belfast, Belfast BT9 5HN, UK

11

4. Lake Ecosystems Group, Centre for Ecology & Hydrology (CEH Lancaster), Lancaster

12

Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, UK

13

14

Abstract

15

Little is known about long-term ecological responses in lakes following red mud pollution.

16

Among red mud contaminants, arsenic (As) is of considerable concern. Determination of the

17

species of As accumulated in aquatic organisms provides important information about the

18

biogeochemical cycling of the element and transfer through the aquatic food-web to higher

19

organisms. We used coupled ion chromatography and inductively coupled plasma mass

20

spectrometry (ICP-MS) to assess As speciation in tissues of five macrophyte taxa in

21

Kinghorn Loch, UK, 30 years following the diversion of red mud pollution from the lake.

22

Toxic inorganic As was the dominant species in the studied macrophytes, with As species

23

concentrations varying with macrophyte taxon and tissue type. The highest As content

24

measured in roots of Persicaria amphibia (L.) Gray (87.2 mg kg-1) greatly exceeded the 3 –

25

10 mg kg-1 range suggested as a potential phytotoxic level. Accumulation of toxic As species *

Corresponding author. Email: [email protected], tel: +44 (0)131 4454343, fax: +44 (0)131 4453943 ACS Paragon Plus Environment

Environmental Science & Technology

26

by plants suggested toxicological risk to higher organisms known to utilise macrophytes as a

27

food source.

28

29

Introduction

30

The estimated global production of red mud, a by-product of alumina production, is ~120

31

million t a-1.1 In October 2010, failure of a containment reservoir in Ajka, Western Hungary,

32

resulted in the release of ~1 million m3 of red mud waste, contaminating the Marcal River

33

(catchment area 3078 km2) and entering the Danube River.2 The Hungarian red mud spill

34

raised concerns about inappropriate storage of red mud and the impact of the waste on the

35

receiving environment. However, little is known about the geochemical behaviour of red mud

36

in freshwaters2 or of the short- and long-term ecological impacts and likelihood of recovery

37

following its release into the environment. This is conspicuous given that many of its

38

chemical constituents are redox sensitive and so likely to persist in aquatic depositional

39

environments where they can represent an environmental and human health risk.

40

Red mud is highly alkaline due to the addition of sodium hydroxide (NaOH) during the

41

production process and contains metal oxides and elevated concentrations of a range of minor

42

trace elements3,4,5 that can be toxic to aquatic organisms. Initial research after the Ajka

43

accident focused on the short-term impact of the pollution on freshwaters. Mayes et al.6

44

reported elevated concentrations of some contaminants, e.g. arsenic (As), vanadium (V),

45

chromium (Cr) and nickel (Ni), in fluvial sediment downstream of the spill. The association

46

of these elements mainly with residual phases suggests limited potential for their mobilisation

47

in the environment. However, in depositional zones, release of these elements may be

48

expected.6 Furthermore, river sediments contaminated with constituents of red mud can have

49

pronounced toxic effects, for example, causing reduced bioluminescence of Vibrio fischeri

2 ACS Paragon Plus Environment

Page 2 of 29

Page 3 of 29

Environmental Science & Technology

50

and growth of Lemna minor and Sinapis alba.2 In aquatic ecosystems with short residence

51

times, the long-term effects of pollution might be spatially limited to depositional zones,

52

allowing system recovery.2 However, the residence time of pollutants in higher retention time

53

aquatic ecosystems can exceed those in fluvial systems.7,8 Therefore, long-term monitoring of

54

the red mud impact on aquatic life is particularly important in lakes that can have potentially

55

longer time-scales of recovery.

56

Among red mud contaminants, As is of considerable concern. It is a toxic element,9 with high

57

concentrations in the aquatic environment posing an environmental and human health risk in

58

many countries, e.g. in Pakistan, Bangladesh, India, Taiwan,10 Japan,11 China12 and the

59

USA.13 Arsenic concentrations in contaminated groundwater were reported of up to 1 mg L-1

60

in some areas of Bangladesh and 3 mg L-1 in Vietnam,14 whilst As concentration of 792 mg

61

kg-1 was measured in surface sediment in Lake Biwa, Japan.11 In macrophytes, uptake of As

62

can reduce phosphorus (P), nitrogen (N), potassium (K), chlorophyll a and protein content in

63

tissues and, due to the chemical similarity of As to P, can interfere with some biochemical

64

reactions.15

65

Concentrations of contaminants accumulated by plants can be higher than in water, but lower

66

than in bed sediments.16 The bioavailability of trace elements to plants can be regulated by a

67

range of site specific factors including their concentration in the environment, trace element

68

speciation, exposure time, and absorption mechanism.16 For example, uptake of the inorganic

69

As species, arsenate, occurs through phosphate uptake pathways and has been shown to be

70

negatively correlated with phosphate uptake by the macrophyte Spirodela polyrhiza L.9 In

71

addition, the capacity of aquatic plants to sequester and accumulate metals is affected by

72

many factors, such as plant growth rate, biomass accumulation and affinity for metal

73

uptake.15 Previous studies have shown that As bioaccumulation varies among macrophyte

74

species and among aquatic plant tissues.15-18 3 ACS Paragon Plus Environment

Environmental Science & Technology

75

Arsenic can occur in inorganic and organic chemical forms, or species, which are associated

76

with different levels of toxicity.19 For example, the inorganic species arsenite (As(III)) is

77

more toxic than organic arsenobetaine to plants and animals.19 The uptake mechanism20 and

78

level of accumulation in plants19,21 also vary between As species. Significant differences

79

between concentrations of different As species have been reported in rice (Oryza sativa L.),

80

with the predominant form being inorganic As.21,22

81

Determination of As speciation in plants is important for assessing the plant As toxicity to

82

consumers at higher levels of the food chain.23-25 Most previous research on As species in

83

plants has focused on crops and As speciation in plants in the aquatic environment has not

84

been extensively studied, with most of the existing knowledge based on controlled laboratory

85

experiments.9,18,20 Consequently, little is known about variation of individual As species

86

between tissues of aquatic plants. Inorganic and organic As species have been determined

87

previously in whole macrophytes9,19,26, but concentrations of As species have not been

88

examined in different plant tissues. Determination of the species of As accumulated in

89

macrophytes allows for more accurate assessment of the environmental risk that increases

90

with the occurrence of inorganic As and is particularly important at sites where fish and

91

waterfowl are used for human consumption.

92

We assessed the impact of As on five macrophyte taxa - three submerged species

93

(Potamogeton pectinatus L., Elodea nuttallii (Planch) H. St. John, Myriophyllum spicatum

94

L.), one rooted, floating-leaved species (Persicaria amphibia (L.) Gray) and one multicellular

95

algae (Chara spp.) in Kinghorn Loch 30 years after the diversion of red mud leachate.

96

Arsenic speciation analysis was applied to quantify inorganic As (arsenite, As(III) and

97

arsenate, As(V)) and four organic As species: arsenobetaine, dimethylarsinic acid (DMA),

98

monomethylarsonic acid (MMA) and tetramethylarsonium ions (Tetra). Based on the results

99

of previous studies on total As accumulation in macrophytes,15-17 As speciation in rice21 and 4 ACS Paragon Plus Environment

Page 4 of 29

Page 5 of 29

Environmental Science & Technology

100

terrestrial plants14 and As species uptake by macrophytes in controlled laboratory

101

experiments,9,18,20 the following hypotheses were tested: (1) macrophytes in Kinghorn Loch

102

accumulate higher concentrations of inorganic compared to organic As species, (2)

103

accumulation of As species varies between above-sediment tissues (leaves and stems) of

104

macrophytes and among macrophyte taxa, and (3) accumulation of As species in P. amphibia

105

is greatest in the roots of the plant compared to the above-sediment tissues. This work

106

provides the first comprehensive assessment of As accumulation and speciation in aquatic

107

macrophytes following red mud pollution.

108

109

Materials and Methods

110

Study site

111

Kinghorn Loch is a small lake of surface area 11.3 ha, mean depth 4.5 m and maximum

112

depth 12.8 m, situated in Fife, Scotland (56o10ʹN; 3o11ʹW). The lake received highly alkaline

113

leachate from a nearby red mud landfill site from 1947 to 1983 when the discharge was

114

diverted. Caustic liquor reaching the lake consisted of a highly alkaline solution of NaOH and

115

carbonate, with a mean pH of 12.1. It contained high concentrations of dissolved aluminium

116

(Al; 137 mg L-1), As (3.56 mg L-1), vanadium (V; 5.3 mg L-1), phosphate (PO4-P; 2.95 mg L-

117

1

118

the loch sporadically, accounted for most of the elevated input of iron (Fe).4 The

119

physicochemical pathways of pollutant transport within the bed sediments of the loch have

120

been discussed in detail in Edwards (1985)4. Long-term monitoring of water chemistry of the

121

loch was initiated in 1980 by the Forth River Purification Board and continued by the

122

Scottish Environment Protection Agency (SEPA). The pollution led to intense algal blooms,

123

fish kills and severe reduction of zooplankton, macroinvertebrate and macrophyte species

), sulfate (SO4-S; 154 mg L-1) and chloride (Cl; 67.8 mg L-1). Red mud solids, released to

5 ACS Paragon Plus Environment

Environmental Science & Technology

124

diversity and biomass.4 By 1985, two years after the diversion of the leachate from the lake, a

125

collapse in the phytoplankton activity, development of zooplankton and an increase in

126

abundance of benthic macroinvertebrates (though no increase in species richness) were

127

observed.4 Bioaccumulation studies of the plankton and macroinvertebrate populations in

128

1985 indicated no significant As bioaccumulation in Kinghorn Loch.4

129

A pilot survey was conducted in 2013 to assess metal concentrations in surface waters and

130

bed sediments.27 Total As concentrations in lake surface water and bottom water (1 cm above

131

sediment; sampled July 2013; Site 1; Figure 1) were 14.9 µg L-1 and 14.8 µg L-1 respectively,

132

and did not exceed Standards for Protection of Aquatic Life in the UK (50 µg L-1).28

133

Concentrations of As in lake surface sediment at Site 1 (87 mg kg-1) and mean As

134

concentration from 6 sites across the lake (160 mg kg-1)27 in July 2013 exceeded the

135

Canadian Sediment Quality Guidelines for Protection of Aquatic Life, which predicts toxicity

136

from sediment concentrations ≥ 17 mg kg-1 of As29. Study of As release from Kinghorn Loch

137

sediment into water conducted in laboratory controlled experiments indicated seasonal

138

mobilisation of As under reducing conditions.27

139

Macrophyte sampling

140

Macrophyte sampling was conducted on 18 July 2013 when whole plants were collected by

141

hand and using a double-headed rake from a boat at three sites in Kinghorn Loch

142

(56o40’26’’N; 3o11’34’’W (Site 1); 56o40’18’’N; 3o11’33’’W (Site 2); 56o40’22’’N; 3o11’16’’W

143

(Site 3); Supporting Information Figure S1). The sites were chosen to represent areas at

144

different distances (approximately 100, 250 and 430 m for Site 1, 2 and 3, respectively) and

145

directions from the NW part of the lake, where the pollution entered the waterbody. Between

146

three and ten plants per taxa (depending on the species specific volume of fresh plant

147

material) were collected at each site. Samples represented the five most abundant macrophyte 6 ACS Paragon Plus Environment

Page 6 of 29

Page 7 of 29

Environmental Science & Technology

148

taxa in Kinghorn Loch – P. amphibia, P. pectinatus, E. nuttallii, M. spicatum and Chara spp.

149

– as determined by a full lake survey conducted on 18 July 2013 following the procedure

150

outlined in Gunn et al.30

151

Sample preparation

152

The macrophytes were stored in polyethylene bags at 4oC until processing in the laboratory

153

within 24 hours. The plant tissues were placed into bags containing distilled water and

154

manually shaken, repeatedly, to remove sediment, macroinvertebrates and epiphytic biofilms.

155

We acknowledge that this approach may not have removed entirely epiphytic organisms

156

although others have reported near complete removal of this community following similar

157

treatments, as well as plant tissue damage under severe agitation31. To test for any variation

158

in As accumulation in the different parts of macrophytes, P. pectinatus, E. nuttallii and M.

159

spicatum samples were divided into leaves and stems, and samples of P. amphibia, the only

160

collected species with well-developed roots, into leaves, stems and roots. Axes and branches

161

of the multicellular algae Chara spp. were also separated and are referred to as stems and

162

leaves, respectively, for the purpose of statistical analysis. Samples of each macrophyte tissue

163

type for each species were combined by site from a number of individual plants to obtain

164

enough dry material for As analyses. Samples were then oven dried at 80oC and ground using

165

a Retsch mixer mill MM200.

166

Chemical analysis

167

Three replicate samples of each tissue type from each macrophyte species were analysed.

168

Approximately 100 ± 5 mg of each powdered sample was digested with 1% nitric acid using

169

a microwave digester (CEM Mars 6 1800W). Arsenic speciation was determined by ion

170

chromatography (Thermo Dionex IC5000 Ion Chromatograph) coupled to inductively

7 ACS Paragon Plus Environment

Environmental Science & Technology

171

coupled plasma mass spectrometry (Thermo Scientific iCap Q ICP-MS). Arsenic species in

172

the solutions were identified by comparing their retention times with those of standards

173

including inorganic As (As(III) and As(V)), arsenite, DMA, MMA and Tetra and quantified

174

by calibration curves with peak areas. Species with retention times not matching any of the

175

standards were classified as unknown species. Total identified As species were calculated as

176

the sum of identified inorganic and organic As species. The detection limit for all As species

177

was 0.001 mg kg-1. The As species concentrations measured in duplicate analyses of the

178

Certified Reference Material (CRM; NIST 1568b Rice flour) conducted in the same manner

179

were within 25% of the certified values. The certified and measured values of As species in

180

the CRM are listed in Table 1. The CRM did not contain arsenobetaine and Tetra. The

181

method for determination of As speciation is described in detail in the Supporting

182

Information.

183

Statistical analyses

184

The means of three replicate samples were used for all statistical analyses. Concentrations of

185

different As species in P. amphibia tissues (leaves and stems) were analysed together with

186

data for the other macrophytes species to examine across species variation in the above-

187

sediment parts of macrophytes, and separately (concentrations in leaves, stems and roots) to

188

test for differences between As concentrations in below- and above-sediment parts of P.

189

amphibia.

190

A one-sided two sample t-test was used to test whether the mean concentration of inorganic

191

As was greater than the mean concentration of total organic As in the above-sediment tissues

192

of macrophytes and also whether below-sediment surface tissues of P. amphibia contained

193

higher concentrations of As species than above-sediment tissues.

8 ACS Paragon Plus Environment

Page 8 of 29

Page 9 of 29

Environmental Science & Technology

194

Mixed effect modelling was conducted to examine variations in concentrations of each As

195

species across macrophyte species and tissue type (within shoots). Root samples were not

196

included in these models, as they were only available for one species. Model validation was

197

conducted on the final models. Homogeneity of variance was assessed by plotting residuals

198

versus fitted values and the normality assumption was evaluated by plotting theoretical

199

quantiles versus standardized residuals (Q-Q plots). In models with all macrophyte species,

200

several response variables (i.e. inorganic As, arsenobetaine, total organic and the sum of all

201

identified As species) were log10 transformed to meet homogeneity and normality

202

assumptions. The random effect part of the model allowed for variations among sites and

203

incorporated a split plot design of the data. The analysis started with the model containing

204

both nominal fixed explanatory variables (i.e. macrophyte species and macrophyte tissue) and

205

the two-way interaction between these two terms. The model selection process followed the

206

procedure described in Zuur et al.32 Maximum likelihood ratio (ML) tests were performed,

207

using the ANOVA function, to select the best-fit model by comparing AIC values and to

208

determine the significance (P < 0.05) of dropped terms. The final model was re-run using

209

restricted maximum likelihood (REML). Statistical analyses were conducted using R version

210

3.0.1,33 using the ‘nlme’ package34 for the mixed modelling.

211

Results

212

Difference between inorganic and organic As concentrations across macrophyte taxa

213

Figure 1 shows variations in As species concentrations across the five macrophyte taxa and

214

different plant tissues of each of the taxa. The above-sediment parts of the five macrophyte

215

species in samples combined across sampling sites contained significantly higher

216

concentrations of inorganic As species than total organic As, with mean values of 8.80 mg

217

kg-1 d.w. (s.d. 13.8) and 0.56 mg kg-1 d.w. (s.d. 0.44), respectively (Table 2). Higher

9 ACS Paragon Plus Environment

Environmental Science & Technology

218

concentrations of inorganic As were measured compared to total organic As concentrations in

219

both tissues of all macrophytes species (Figure 1, Table S1). P. amphibia also contained

220

significantly higher concentrations of inorganic As than total organic As, with mean values of

221

40.0 mg kg-1 d.w. (s.d. 65.7) for inorganic and 0.25 mg kg-1 d.w. (s.d. 0.11) for organic forms

222

(Table 2), respectively, calculated as the arithmetic mean of above and below-sediment

223

surface tissues As concentrations.

224

Differences in As species accumulation in above-sediment macrophyte tissues

225

The lowest mean concentrations of inorganic As in the above sediment-surface tissues were

226

measured in the leaves and stems of P. amphibia (0.76 mg kg-1 ± 0.14 and 1.07 mg kg-1 ±

227

0.29, respectively) and the highest in leaves of E. nuttallii (45.1 mg kg-1 ± 20.7; Figure 1,

228

Table S1). Two organic As species (MMA and Tetra) were below the limit of detection in all

229

tissue types of Chara spp., with MMA also not detectable in leaves of M. spicatum. Mean

230

concentrations of the four organic As species ranged from 0.01 mg kg-1 d.w. (DMA in Chara

231

sp. branches, MMA in both tissues of P. amphibia, Tetra in P.amphibia leaves) to 1.16 mg

232

kg-1 (arsenobetaine in Chara spp. branches). Unknown As species were present in the leaves

233

of P. pectinatus and M. spicatum and in both tissues of Chara spp., with the highest mean

234

concentration (1.04 mg kg-1 ± 0.47) measured in the latter species.

235

The model selection process indicated a model with plant tissue, plant species and the

236

interaction term included as an optimal one for inorganic As, arsenobetaine, MMA, Tetra,

237

total organic As, and all identified As species (Table S2). Due to a lack of a significant effect,

238

the interaction term was omitted from the model for unknown As species. None of the

239

explanatory variables was found to have a significant association with plant DMA

240

concentration.

10 ACS Paragon Plus Environment

Page 10 of 29

Page 11 of 29

Environmental Science & Technology

241

E. nuttallii had significantly higher (estimate: 1.79, S.E.: 0.27, t: 6.67, P: