Bull Environ Contam Toxicol DOI 10.1007/s00128-015-1520-x
Trace Elements in the Marine Sediments of the La Paz Lagoon, Baja California Peninsula, Mexico: Pollution Status in 2013 Habacuc Pe´rez-Tribouillier1 • Evgueni Shumilin1 Griselda Margarita Rodrı´guez-Figueroa1
•
Received: 15 October 2014 / Accepted: 7 March 2015 Ó Springer Science+Business Media New York 2015
Abstract To determine the actual concentrations of trace elements in surface sediments from the La Paz Lagoon, as well as their associations and possible origins, 91 sediment samples were analyzed for more than 50 elements using a combination of ICP-MS and ICP-AES. The results of a principal component analysis are used to distinguish four associative groups within the elements. Natural enrichment of As, Cd and U occurs due to the supply of weathered phosphorites from the El Cien formation located to the north-west of the lagoon. Sediment quality indices for potentially toxic trace elements do not show any probable impact on the biota of the lagoon. Only the concentrations of As in 30 % of the stations and Cu in 20 % of them exceed related effect range low levels. The highest concentration of Pb (36.8 mg kg-1) was measured in the sediments near the City of La Paz. Keywords Trace elements Sediments Pollution status La Paz Lagoon Baja California peninsula Some trace elements can pollute coastal marine ecosystems, creating a risk for the marine biota and local population (Gerlach 1981). Sediments are very useful for estimating the pollution of coastal environments by potentially toxic trace elements (PTTEs) (Salomons and Fo¨rstner 1984; Caccia et al. 2003; Green-Ruiz and Pa´ez-Osuna 2004 ; Kumar et al. 2013). The geochemistry of trace metals in the coastal zones
& Evgueni Shumilin [email protected] 1
Instituto Polite´cnico Nacional- Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, colonia Playa Palo de Santa Rita, Apdo postal 592, 23096 La Paz, Baja California Sur, Mexico
of arid environments is strongly influenced by the lithology and weathering of the rocks constituting the drainage basin. Water in dry streams (arroyos) cutting the desertic arid and semi-arid lands appears only very infrequently and transports few weathered rock fragments. The La Paz Lagoon of the Bahı´a de La Paz is an almost enclosed shallow coastal embayment in the semi-arid southwestern Baja California peninsula. It is the neighboring marine environment for La Paz, the capital of the State of Baja California Sur, a fast-growing city with a rapid increase in population over the last few decades. Some geochemical studies of the sediments were conducted in 1995–1996 (Me´ndez et al.1998; Rodrı´guez Meza 1999; Shumilin et al. 2001); however, actual assessment of the sedimentary environment of this lagoon is strongly needed. The aim of this work is to evaluate the concentrations and associations of the elements in the sediments, including their principal spatial distribution patterns, as well as to characterize the actual (year 2013) contamination status of the sediments of the La Paz Lagoon by applying existing sediment quality guidelines.
Materials and Methods The study area and location of the sampling stations is shown in Fig. 1. The samples were collected from the upper layer (1 cm) of sediment by a scuba diver in February 2013. Samples were stored frozen in pre-cleaned polyethylene bags. Once in the laboratory, they were thawed, dried overnight in an oven at 40°C and homogenized in an agate mortar. The elemental composition of the sediments was determined by Actlabs (Ancaster, Ontario, Canada). 250 mg of each sediment sample were digested with a mixture of
123
Bull Environ Contam Toxicol Fig. 1 Study area and location of sediment sampling stations in the La Paz Lagoon, Baja California peninsula
concentrated HCl, HNO3, HClO4 and HF at 260°C until dry and then diluted using aqua regia. Al, Ca, Fe, Mn, P, S and Ti concentrations in final solutions were determined with a Varian ICP-OES analyzer, while other trace element concentrations were measured on a Perkin Elmer Sciex ELAN 9000 ICP-MS instrument. The accuracy was checked using sediment CRMs (NIST 1646a, USA, as well as MESS-3 and PACS-2, National Research Council of Canada). The percentage recoveries ranged from 82 % (As) to 110 % (Cr). Each sample was analyzed three times, and the mean value was calculated. The maximum relative standard deviation (RSD) values of individual samples were less than 4 %. Organic carbon concentrations in the sediments were measured using an ELTRA CS-2000 analyzer with an induction furnace coupled with infrared detector. The associations of the elements in the sediments were evaluated by principal component analysis (factor analysis with Varimax rotation) with Statistica software. Enrichment factors (EF) were calculated using a normalizing terrigenous element of Li, which was the most efficient normalizer in this case (Pe´rez Tribouillier 2014): EF ¼ ðCi =CLi Þsample : ðCi =CLi Þcrust ; where Ci and CLi denote the concentrations of element i and Li, respectively, in the sample and in the average upper continental crust (UCC) (Wedepohl 1995). According to the EF values, there are the following options for the elements in the sediments: (1) EF \ 1 indicates no enrichment; (2) 1 \ EF \ 3 is minor enrichment; (3) 3 \ EF \ 5 is moderate enrichment; (4) 5 \ EF \ 10 is moderately severe enrichment; and (5) 10 \ EF \ 25 is severe enrichment (Sakan et al. 2009). Spatial distributions of the elements’ concentrations were generated using the ‘‘kriging’’ interpolation method in Surfer 12 software.
123
To assess the environmental risk of PPTEs in the sediments, the criteria of the effects range-low (ERL) and effects range-median (ERM) proposed by Long et al. (1995), as well as the Threshold Effects Level (TEL) from the screening quick reference tables (SQuiRTs, Buchman 1999) were used in this study.
Results and Discussion The elemental composition of the surface marine sediments from the La Paz Lagoon is presented in complete form by Pe´rez Tribouillier (2014). Enrichment factors of some trace elements in the sediments of the La Paz Lagoon are shown in Table 1. On basis of their average EF values, these elements can be ordered in sequence: Se [ As [ Cd [ U [ Cu [ Pb. According to above-mentioned classification of EFs, Se shows severe enrichment. Previous studies have shown high concentrations of Se in marine sediments along the Baja California peninsula most probably due to ancient volcanic input from the land (Shumilin et al. 2000), and therefore it is not strange that the sediments of the La Paz Lagoon are enriched in this element. Arsenic indicates moderately severe enrichment and Cd is moderately enriched in the La Paz Lagoon sediments. Minor enrichment is observed for Cu and U, and the average EF value of Pb does not show any enrichment. The full dataset of the elemental composition of the marine sediments from the La Paz Lagoon was processed using principal component analysis. The results obtained are shown in Table 2. Three factors control the variance of the element concentrations: factor 1 (41.4 % of the total variance), factor 2 (22.6 % of the total variance) and factor 3 (12 % of the total variance). Taking into account the elements with high positive or negative scores ([±0.7),
Bull Environ Contam Toxicol Table 1 Enrichment factors of some trace elements in the sediments of the La Paz Lagoon
EF range
As
Cd
Cu
Pb
Se
U
Min
0.9
0.3
0.3
0.3
1.3
0.2
Max
20.1
16.7
5.2
3.0
67.8
5.1
Average ± SD
5.2 ± 4.5
3.6 ± 3.5
1.2 ± 0.7
0.8 ± 0.5
10.3 ± 9.1
1.3 ± 1.1
SD standard deviation
Table 2 Results of the principal components analysis applied to chemical composition of surface sediments of the La Paz Lagoon
Element
Factor 1
Factor 2
Factor 3
Element
Factor 1
Factor 2
Factor 3
Al
0.19
0.00
0.80
La
0.98
-0.07
0.07
As
0.94
-0.03
-0.02
Li
-0.01
0.90
0.26 0.13
Be
0.02
0.13
0.88
Mn
0.61
0.73
Ca
-0.26
-0.17
20.83
Nb
-0.21
0.74
0.42
Cd
0.95
-0.07
-0.12
Ni
0.39
0.73
-0.47
Co
0.40
0.81
0.20
P
0.94
-0.13
-0.12
-0.42
-0.07
20.80
S
-0.17
0.76
-0.45
Cr
0.81
0.17
0.03
Ti
-0.04
0.80
0.44
Cs
-0.05
0.89
0.25
U
0.86
-0.04
-0.33
Cu
-0.07
0.78
0.11
V
0.74
0.55
0.18
Fe
0.45
0.82
0.25
Y
0.99
0.00
Corg
% of total variance
41.4
22.6
12.0
% of total variance
41.4
22.6
0.03 12.0
The scores values larger than the module of 0.70 are shown in bold because they are considered to be more important statistics
four groups of elements can be distinguished, leading to some ideas about their origins. A noticeable feature of the sediments of the La Paz Lagoon is the existence of the first association of the elements, composed of As, Cd, Cr, P, U, V, La and lanthanides. The presence of phosphorus in this group of elements suggests that these elements are bound within the phosphorites that appear as weathering and erosion products of the El Cien geological formation located north–west of the La Paz Lagoon (Piper 1991). Factor 1 containing the first association of elements has high scores for the stations located mainly around the Mogote sandbar and in the tidal channel where only medium and coarse sands ([63 lm) are accumulated due to higher water current velocities (Fig. 2). Factor 2 embracing the second association of elements (Co, Cs, Cu, Fe, Li, Nb, Ni, S and Ti) is important for the stations located in the deepest part of the lagoon as well as in its southern part (Fig. 2). Both areas are characterized by a predominance of fine sediments (\63 lm) deposited here because of low water current velocities, a clear indication that these terrigenous elements supplied by arroyos are incorporated into fine sediments. The third association includes the elements Al and Be, also from a terrigenous source. Calcium and organic carbon belong to the fourth association, which can be related to modern or ancient sedimentary material of marine biogenic origin, including calcareous material, such as shell fragments and carbonate skeletons or detritus of marine biota.
The typical pattern of the spatial distribution of concentrations of the elements belonging to the first association is shown in Fig. 3a–c. The common feature of these distributions is elevated concentrations in shallow northern portion of the lagoon and along the narrow part of the El Mogote peninsula. A similar pattern of spatial distribution can also be observed for the enrichment factors of the elements of this association (Pe´rez Tribouillier 2014). All of these observations can be explained if it is presumed that the source of these elements is the phosphorites of the El Cien formation (Piper 1991), which were eroded, transported to the coastal sediments of the Bahı´a de La Paz by the arroyos, resuspended by wave actions and moved by littoral currents initially southward and then eastward to the coastal line off the Estero Zacatecas and El Mogote peninsula (Salinas Gonza´lez 2000), accumulated in the sandy coastal dunes, and then transferred to the northern part of the La Paz Lagoon by wind. Regarding the status of the contamination of the lagoon sediments by PTTEs, it was concluded from the results of the study of Cd, Cu, Fe, Pb, Mn and Zn in the sediments from eight stations collected in the La Paz Lagoon in 1995 that, in general, anthropogenic influence in the lagoon was not appreciable (Me´ndez et al. 1998). Our data, with many more elements and sampling stations from the sediments collected in 2013, mainly coincide with these previous findings. Arsenic and Cd are still appearing from the
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Bull Environ Contam Toxicol Fig. 2 Distribution of PCA factors in the La Paz Lagoon. Light blue indicates factor 1 (phosphorite related), medium blue corresponds to the transition stations and dark blue refers to factor 2 dominated stations (fine grain size related) (Color figure online)
Fig. 3 Spatial distribution of the concentration of selected elements in surface sediments of the La Paz Lagoon: a phosphorus, b arsenic, c cadmium, d lead
natural land-based sources, most likely supplied by weathering and transport from phosphorite-containing rocks (Me´ndez et al. 1998; Piper 1991; Shumilin et al. 2001). The important anthropogenic contaminant Pb occurs mainly in concentrations close to the average UCC abundance (17 mg kg-1, Wedepohl 1995). The only site in the tidal channel, close to the central part of the City of La Paz, displays somewhat elevated Pb content in the surface
123
sediments (36.8 mg kg-1) (Fig. 3d). This site most likely receives, after infrequent but intensive rainfall, coarse material from the adjacent land, which was previously affected by the supply of lead from gasoline combustion when leaded gasoline was actively used in the city’s vehicular traffic. The location of the site with the maximum content of Pb in the sediments is most likely controlled by the
Bull Environ Contam Toxicol Table 3 Comparison of the concentration of selected PTTEs in the sediments of the La Paz Lagoon (mg kg-1) with the sediment quality criteria of Long et al. (1995) and the SQuiRTs (Buchman 1999)
As
Cd
Cr
Cu
Pb
Ni
Zn
Mean ± SD
8.0 ± 5.5
0.3 ± 0.2
29 ± 21
18.0 ± 6.3
11.1 ± 4.9
11.3 ± 4.2
49 ± 38
UCC
2.0
0.102
35
14.3
17
18.6
52
TEL
7.24
0.676
52.3
18.7
30.24
15.9
124
ERL
8.2
1.2
81
34
46.7
20.9
150
ERM
70
9.6
370
270
218
51.6
410
SD standard deviation
Fig. 4 Evaluation of sediment quality in the sediments of the La Paz Lagoon according to the criteria of Long et al. (1995) for: a arsenic (mg kg-1), b copper (mg kg-1)
resuspension of the sediments and littoral transport inside the channel and is most likely decreasing from the high values of 50–89 mg kg-1 reported previously for the 1996 sampling (Shumilin et al. 2001). The pollution status of the surface sediments of the La Paz Lagoon, estimated with Sediment Quality Guidelines (Long et al. 1995) and the SQuiRTs (Buchman 1999) for PTTEs can be seen in Table 3. Average concentrations of As, Cd and Cu exceed their respective average upper continental crust abundances (Wedepohl 1995). However, this table shows that the average concentrations only of As are slightly higher than the TEL and close to the ERL value for this element, and the average concentrations of other PTTEs are below related TEL and ERL values. Considering the spatial distributions of the concentrations of PTTEs along with sediment quality criteria (Fig. 4) allows for the observation that As and Cu concentrations in the sediments of the lagoon surpass ERL values for these elements at only 30 % and 20 % of the total number of stations, respectively (Pe´rez Tribouillier 2014). The highest Pb concentration in the sediments (36.8 mg kg-1) slightly exceeds the TEL but is also lower than the ERL value for this element (46.7 mg kg-1). Such estimation allows us to conclude the anthropogenic impact of La Paz City on the La Paz Lagoon with respect to the concentrations of PTTEs in the sediments is still almost negligible.
Acknowledgments This study was supported by Project 20131764, ‘‘Arsenic and other potentially toxic elements in the sediments of the La Paz Lagoon: actual levels and historical record of natural and anthropogenic contamination’’ from the Secretarı´a de Posgrado e Investigacio´n of the Instituto Polite´cnico Nacional of Mexico.
References Buchman MF (1999) NOAA Screening Quick Reference Tables. NOAA HAZMATReport 99-1. Coastal Protection and Restoration Division, National Oceanic and Atmospheric Administration, Seattle Caccia VG, Millero F, Palanques A (2003) The distribution of trace metals in Florida Bay sediments. Mar Pollut Bull 46:1420–1433 Gerlach SA (1981) Marine pollution: diagnosis and therapy. Springer, Berlin Green-Ruiz C, Pa´ez-Osuna F (2004) Potential bioavailability of heavy metals in surface sediments from the Altata-Ensenada del Pabello´n Lagoon, SE Gulf of California. J Coast Res 20:1126–1134 Kumar A, Singhal RK, Sabyasachi R, Ravi PM (2013) Spatial geochemical variation of major and trace elements in the marine sediments of Mumbai Harbor Bay. Environ Earth Sci 70:3057–3066 Long ER, Macdonald DD, Smith SL, Calder FD (1995) Incidence of adverse biological effects within ranges of chemical concentrations in marine and estuarine sediments. Environ Manag 19:81–97 Me´ndez L, Acosta B, Alvarez-Castan˜eda ST, Lechuga-Deve´ze CH (1998) Trace metal distribution along the southern coast of the Bahia de La Paz (Gulf of California), Mexico. Bull Environ Contam Toxicol 61:616–622
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Bull Environ Contam Toxicol Pe´rez Tribouillier HU (2014) Niveles actuales e historia de acumulacio´n de elementos de origen natural y antropoge´nico en los sedimentos de la Laguna de La Paz, Baja California Sur, Me´xico. M.S. Thesis. Centro Interdisciplinario de Ciencias Marinas. Instituto Polite´cnico Nacional, La Paz, Baja California Sur, Mexico (in Spanish) Piper DZ (1991) Geochemistry of a Tertiary sedimentary phosphate deposit: Baja California Sur, Mexico. Chem Geol 92:283–316 Rodrı´guez Meza GD (1999) Metales pesados en sedimentos de la Ensenada de La Paz, B.C.S., Me´xico. M.S. Thesis. Centro Interdisciplinario de Ciencias Marinas. Instituto Polite´cnico Nacional, La Paz, Baja California Sur, Mexico (in Spanish) Sakan SM, Dordevic DS, Manojlovic DD, Predrag PS (2009) Assessment of heavy metal pollutant accumulation in the Tisza river sediments. J Environ Manag 90:3382–3390 Salinas Gonza´lez F (2000) Mezcla turbulenta y transporte de masa en La Bahı´a y Ensenada de La Paz, B.C.S.: experimentacio´n y modelacio´n nume´rica. Ph.D.Thesis. Centro Interdisciplinario de
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Ciencias Marinas. Instituto Polite´cnico Nacional, La Paz, Baja California Sur, Mexico (in Spanish) Salomons W, Fo¨rstner U (1984) Metals in hydrocycle. Springer, Heidelberg Shumilin E, Kalmykov S, Sapozhnikov D, Nava-Sa´nchez E, Gorsline D, Godinez-Orta L, Sapozhnikov Y, Holguin-Quin˜ones O, Rodriguez-Castan˜eda A (2000) Major and trace element accumulation in coastal sediments along southeastern Baja California studied by instrumental neutron activation analysis and 210Pb age-dating. J Radioanal Nucl Chem 246:533–541 Shumilin E, Pa´ez-Osuna F, Green-Ruiz C, Sapozhnikov D, Rodrı´guez-Meza G, Godı´nez-Orta L (2001) Arsenic, antimony, selenium and other trace elements in sediments of the La Paz Lagoon, Peninsula of Baja California, Mexico. Mar Pollut Bull 42:174–178 Wedepohl KH (1995) The composition of the continental crust. Geochim Cosmochim Acta 59:1217–1232
Trace Elements in the Marine Sediments of the La Paz Lagoon, Baja California Peninsula, Mexico: Pollution Status in 2013 Habacuc Pe´rez-Tribouillier1 • Evgueni Shumilin1 Griselda Margarita Rodrı´guez-Figueroa1
•
Received: 15 October 2014 / Accepted: 7 March 2015 Ó Springer Science+Business Media New York 2015
Abstract To determine the actual concentrations of trace elements in surface sediments from the La Paz Lagoon, as well as their associations and possible origins, 91 sediment samples were analyzed for more than 50 elements using a combination of ICP-MS and ICP-AES. The results of a principal component analysis are used to distinguish four associative groups within the elements. Natural enrichment of As, Cd and U occurs due to the supply of weathered phosphorites from the El Cien formation located to the north-west of the lagoon. Sediment quality indices for potentially toxic trace elements do not show any probable impact on the biota of the lagoon. Only the concentrations of As in 30 % of the stations and Cu in 20 % of them exceed related effect range low levels. The highest concentration of Pb (36.8 mg kg-1) was measured in the sediments near the City of La Paz. Keywords Trace elements Sediments Pollution status La Paz Lagoon Baja California peninsula Some trace elements can pollute coastal marine ecosystems, creating a risk for the marine biota and local population (Gerlach 1981). Sediments are very useful for estimating the pollution of coastal environments by potentially toxic trace elements (PTTEs) (Salomons and Fo¨rstner 1984; Caccia et al. 2003; Green-Ruiz and Pa´ez-Osuna 2004 ; Kumar et al. 2013). The geochemistry of trace metals in the coastal zones
& Evgueni Shumilin [email protected] 1
Instituto Polite´cnico Nacional- Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, colonia Playa Palo de Santa Rita, Apdo postal 592, 23096 La Paz, Baja California Sur, Mexico
of arid environments is strongly influenced by the lithology and weathering of the rocks constituting the drainage basin. Water in dry streams (arroyos) cutting the desertic arid and semi-arid lands appears only very infrequently and transports few weathered rock fragments. The La Paz Lagoon of the Bahı´a de La Paz is an almost enclosed shallow coastal embayment in the semi-arid southwestern Baja California peninsula. It is the neighboring marine environment for La Paz, the capital of the State of Baja California Sur, a fast-growing city with a rapid increase in population over the last few decades. Some geochemical studies of the sediments were conducted in 1995–1996 (Me´ndez et al.1998; Rodrı´guez Meza 1999; Shumilin et al. 2001); however, actual assessment of the sedimentary environment of this lagoon is strongly needed. The aim of this work is to evaluate the concentrations and associations of the elements in the sediments, including their principal spatial distribution patterns, as well as to characterize the actual (year 2013) contamination status of the sediments of the La Paz Lagoon by applying existing sediment quality guidelines.
Materials and Methods The study area and location of the sampling stations is shown in Fig. 1. The samples were collected from the upper layer (1 cm) of sediment by a scuba diver in February 2013. Samples were stored frozen in pre-cleaned polyethylene bags. Once in the laboratory, they were thawed, dried overnight in an oven at 40°C and homogenized in an agate mortar. The elemental composition of the sediments was determined by Actlabs (Ancaster, Ontario, Canada). 250 mg of each sediment sample were digested with a mixture of
123
Bull Environ Contam Toxicol Fig. 1 Study area and location of sediment sampling stations in the La Paz Lagoon, Baja California peninsula
concentrated HCl, HNO3, HClO4 and HF at 260°C until dry and then diluted using aqua regia. Al, Ca, Fe, Mn, P, S and Ti concentrations in final solutions were determined with a Varian ICP-OES analyzer, while other trace element concentrations were measured on a Perkin Elmer Sciex ELAN 9000 ICP-MS instrument. The accuracy was checked using sediment CRMs (NIST 1646a, USA, as well as MESS-3 and PACS-2, National Research Council of Canada). The percentage recoveries ranged from 82 % (As) to 110 % (Cr). Each sample was analyzed three times, and the mean value was calculated. The maximum relative standard deviation (RSD) values of individual samples were less than 4 %. Organic carbon concentrations in the sediments were measured using an ELTRA CS-2000 analyzer with an induction furnace coupled with infrared detector. The associations of the elements in the sediments were evaluated by principal component analysis (factor analysis with Varimax rotation) with Statistica software. Enrichment factors (EF) were calculated using a normalizing terrigenous element of Li, which was the most efficient normalizer in this case (Pe´rez Tribouillier 2014): EF ¼ ðCi =CLi Þsample : ðCi =CLi Þcrust ; where Ci and CLi denote the concentrations of element i and Li, respectively, in the sample and in the average upper continental crust (UCC) (Wedepohl 1995). According to the EF values, there are the following options for the elements in the sediments: (1) EF \ 1 indicates no enrichment; (2) 1 \ EF \ 3 is minor enrichment; (3) 3 \ EF \ 5 is moderate enrichment; (4) 5 \ EF \ 10 is moderately severe enrichment; and (5) 10 \ EF \ 25 is severe enrichment (Sakan et al. 2009). Spatial distributions of the elements’ concentrations were generated using the ‘‘kriging’’ interpolation method in Surfer 12 software.
123
To assess the environmental risk of PPTEs in the sediments, the criteria of the effects range-low (ERL) and effects range-median (ERM) proposed by Long et al. (1995), as well as the Threshold Effects Level (TEL) from the screening quick reference tables (SQuiRTs, Buchman 1999) were used in this study.
Results and Discussion The elemental composition of the surface marine sediments from the La Paz Lagoon is presented in complete form by Pe´rez Tribouillier (2014). Enrichment factors of some trace elements in the sediments of the La Paz Lagoon are shown in Table 1. On basis of their average EF values, these elements can be ordered in sequence: Se [ As [ Cd [ U [ Cu [ Pb. According to above-mentioned classification of EFs, Se shows severe enrichment. Previous studies have shown high concentrations of Se in marine sediments along the Baja California peninsula most probably due to ancient volcanic input from the land (Shumilin et al. 2000), and therefore it is not strange that the sediments of the La Paz Lagoon are enriched in this element. Arsenic indicates moderately severe enrichment and Cd is moderately enriched in the La Paz Lagoon sediments. Minor enrichment is observed for Cu and U, and the average EF value of Pb does not show any enrichment. The full dataset of the elemental composition of the marine sediments from the La Paz Lagoon was processed using principal component analysis. The results obtained are shown in Table 2. Three factors control the variance of the element concentrations: factor 1 (41.4 % of the total variance), factor 2 (22.6 % of the total variance) and factor 3 (12 % of the total variance). Taking into account the elements with high positive or negative scores ([±0.7),
Bull Environ Contam Toxicol Table 1 Enrichment factors of some trace elements in the sediments of the La Paz Lagoon
EF range
As
Cd
Cu
Pb
Se
U
Min
0.9
0.3
0.3
0.3
1.3
0.2
Max
20.1
16.7
5.2
3.0
67.8
5.1
Average ± SD
5.2 ± 4.5
3.6 ± 3.5
1.2 ± 0.7
0.8 ± 0.5
10.3 ± 9.1
1.3 ± 1.1
SD standard deviation
Table 2 Results of the principal components analysis applied to chemical composition of surface sediments of the La Paz Lagoon
Element
Factor 1
Factor 2
Factor 3
Element
Factor 1
Factor 2
Factor 3
Al
0.19
0.00
0.80
La
0.98
-0.07
0.07
As
0.94
-0.03
-0.02
Li
-0.01
0.90
0.26 0.13
Be
0.02
0.13
0.88
Mn
0.61
0.73
Ca
-0.26
-0.17
20.83
Nb
-0.21
0.74
0.42
Cd
0.95
-0.07
-0.12
Ni
0.39
0.73
-0.47
Co
0.40
0.81
0.20
P
0.94
-0.13
-0.12
-0.42
-0.07
20.80
S
-0.17
0.76
-0.45
Cr
0.81
0.17
0.03
Ti
-0.04
0.80
0.44
Cs
-0.05
0.89
0.25
U
0.86
-0.04
-0.33
Cu
-0.07
0.78
0.11
V
0.74
0.55
0.18
Fe
0.45
0.82
0.25
Y
0.99
0.00
Corg
% of total variance
41.4
22.6
12.0
% of total variance
41.4
22.6
0.03 12.0
The scores values larger than the module of 0.70 are shown in bold because they are considered to be more important statistics
four groups of elements can be distinguished, leading to some ideas about their origins. A noticeable feature of the sediments of the La Paz Lagoon is the existence of the first association of the elements, composed of As, Cd, Cr, P, U, V, La and lanthanides. The presence of phosphorus in this group of elements suggests that these elements are bound within the phosphorites that appear as weathering and erosion products of the El Cien geological formation located north–west of the La Paz Lagoon (Piper 1991). Factor 1 containing the first association of elements has high scores for the stations located mainly around the Mogote sandbar and in the tidal channel where only medium and coarse sands ([63 lm) are accumulated due to higher water current velocities (Fig. 2). Factor 2 embracing the second association of elements (Co, Cs, Cu, Fe, Li, Nb, Ni, S and Ti) is important for the stations located in the deepest part of the lagoon as well as in its southern part (Fig. 2). Both areas are characterized by a predominance of fine sediments (\63 lm) deposited here because of low water current velocities, a clear indication that these terrigenous elements supplied by arroyos are incorporated into fine sediments. The third association includes the elements Al and Be, also from a terrigenous source. Calcium and organic carbon belong to the fourth association, which can be related to modern or ancient sedimentary material of marine biogenic origin, including calcareous material, such as shell fragments and carbonate skeletons or detritus of marine biota.
The typical pattern of the spatial distribution of concentrations of the elements belonging to the first association is shown in Fig. 3a–c. The common feature of these distributions is elevated concentrations in shallow northern portion of the lagoon and along the narrow part of the El Mogote peninsula. A similar pattern of spatial distribution can also be observed for the enrichment factors of the elements of this association (Pe´rez Tribouillier 2014). All of these observations can be explained if it is presumed that the source of these elements is the phosphorites of the El Cien formation (Piper 1991), which were eroded, transported to the coastal sediments of the Bahı´a de La Paz by the arroyos, resuspended by wave actions and moved by littoral currents initially southward and then eastward to the coastal line off the Estero Zacatecas and El Mogote peninsula (Salinas Gonza´lez 2000), accumulated in the sandy coastal dunes, and then transferred to the northern part of the La Paz Lagoon by wind. Regarding the status of the contamination of the lagoon sediments by PTTEs, it was concluded from the results of the study of Cd, Cu, Fe, Pb, Mn and Zn in the sediments from eight stations collected in the La Paz Lagoon in 1995 that, in general, anthropogenic influence in the lagoon was not appreciable (Me´ndez et al. 1998). Our data, with many more elements and sampling stations from the sediments collected in 2013, mainly coincide with these previous findings. Arsenic and Cd are still appearing from the
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Bull Environ Contam Toxicol Fig. 2 Distribution of PCA factors in the La Paz Lagoon. Light blue indicates factor 1 (phosphorite related), medium blue corresponds to the transition stations and dark blue refers to factor 2 dominated stations (fine grain size related) (Color figure online)
Fig. 3 Spatial distribution of the concentration of selected elements in surface sediments of the La Paz Lagoon: a phosphorus, b arsenic, c cadmium, d lead
natural land-based sources, most likely supplied by weathering and transport from phosphorite-containing rocks (Me´ndez et al. 1998; Piper 1991; Shumilin et al. 2001). The important anthropogenic contaminant Pb occurs mainly in concentrations close to the average UCC abundance (17 mg kg-1, Wedepohl 1995). The only site in the tidal channel, close to the central part of the City of La Paz, displays somewhat elevated Pb content in the surface
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sediments (36.8 mg kg-1) (Fig. 3d). This site most likely receives, after infrequent but intensive rainfall, coarse material from the adjacent land, which was previously affected by the supply of lead from gasoline combustion when leaded gasoline was actively used in the city’s vehicular traffic. The location of the site with the maximum content of Pb in the sediments is most likely controlled by the
Bull Environ Contam Toxicol Table 3 Comparison of the concentration of selected PTTEs in the sediments of the La Paz Lagoon (mg kg-1) with the sediment quality criteria of Long et al. (1995) and the SQuiRTs (Buchman 1999)
As
Cd
Cr
Cu
Pb
Ni
Zn
Mean ± SD
8.0 ± 5.5
0.3 ± 0.2
29 ± 21
18.0 ± 6.3
11.1 ± 4.9
11.3 ± 4.2
49 ± 38
UCC
2.0
0.102
35
14.3
17
18.6
52
TEL
7.24
0.676
52.3
18.7
30.24
15.9
124
ERL
8.2
1.2
81
34
46.7
20.9
150
ERM
70
9.6
370
270
218
51.6
410
SD standard deviation
Fig. 4 Evaluation of sediment quality in the sediments of the La Paz Lagoon according to the criteria of Long et al. (1995) for: a arsenic (mg kg-1), b copper (mg kg-1)
resuspension of the sediments and littoral transport inside the channel and is most likely decreasing from the high values of 50–89 mg kg-1 reported previously for the 1996 sampling (Shumilin et al. 2001). The pollution status of the surface sediments of the La Paz Lagoon, estimated with Sediment Quality Guidelines (Long et al. 1995) and the SQuiRTs (Buchman 1999) for PTTEs can be seen in Table 3. Average concentrations of As, Cd and Cu exceed their respective average upper continental crust abundances (Wedepohl 1995). However, this table shows that the average concentrations only of As are slightly higher than the TEL and close to the ERL value for this element, and the average concentrations of other PTTEs are below related TEL and ERL values. Considering the spatial distributions of the concentrations of PTTEs along with sediment quality criteria (Fig. 4) allows for the observation that As and Cu concentrations in the sediments of the lagoon surpass ERL values for these elements at only 30 % and 20 % of the total number of stations, respectively (Pe´rez Tribouillier 2014). The highest Pb concentration in the sediments (36.8 mg kg-1) slightly exceeds the TEL but is also lower than the ERL value for this element (46.7 mg kg-1). Such estimation allows us to conclude the anthropogenic impact of La Paz City on the La Paz Lagoon with respect to the concentrations of PTTEs in the sediments is still almost negligible.
Acknowledgments This study was supported by Project 20131764, ‘‘Arsenic and other potentially toxic elements in the sediments of the La Paz Lagoon: actual levels and historical record of natural and anthropogenic contamination’’ from the Secretarı´a de Posgrado e Investigacio´n of the Instituto Polite´cnico Nacional of Mexico.
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