Indian Journal Journal of Geo-Marine of Marine Sciences Sciences Vol. 43(6), June 2014, pp.1027-10351021-1029 Environmental significance of heavy metals in leaves and stems of Kerala mangroves, SW coast of India A. Badarudeen, " K. Sajan, , Reji Srinivas.? K. Maya? & D. Padmalal" 'Departmentment of Marine Geology and Geophysics, School of Marine Sciences, Cochin University of Science and Technology, Kochi 682 016, India. 2Centre for.Earth Science Studies, Thiruvananthapuram- 695031, Kerala, India [E-Mail: [email protected]] Received 17 December 2012; revised 2 May 2014 Out of the seven heavy metals (Fe, Mn, Co, Pb, Cd, Cu and Zn) studied in the leaves and stems of mangroves and mangrove associates of Veli (9 species), Kochi (5 species) and Kannur (9 species) regions, Cerbera odol/am, a typical mangrove associate that spread in Veti, accounts for the highest contents of Mn and Cd. Other plant species do not show any specific heavy metal enrichment pattern in the coastal segments chosen for the present study. A comparative evaluation of heavy metal contents in the vegetal parts (leaves and stems) with that of the sediment substratum reveals that, almost all metals are concentrated in the former than latter. [Keywords: Coastal sedimentary environments, Mangroves and mangrove associates, Heavy metals, Southwestern coast of India.] Introduction are some of the other adaptations exhibited by mangrove plants to thrive in harmony within the Mangroves, a group of salt-tolerant plant intertidal zone", Studies on the geochemical communities occurring in the land-sea interface, characteristics of mangrove environment show that contribute significant quantities of organic matter and, major, micro and trace nutrient elements to the coastal/ sediments in this zone could sink a substantial quantity nearshore environments-" Many of the world's of toxic contaminants, particularly heavy metals, important mangrove populations are at the verge of without much damage to the vegetation":". Mangrove deterioration':'. Mangrove ecosystem is very fragile vegetation plays a significant role in regulating till owing to the peculiar conditions of hydrodynamics concentration of major and micro-nutrient elements and sedimentation. These inter-tidal forest ecosystems (including heavy metals) in soil/sediments of its support diverse communities of terrestrial and aquatic habitat. organisms of direct and indirect socio-economic Mangroves of Kerala in the south western coast values": of India are at the verge of severe degradation Mangroves act as a buffer between transitional, consequent to human interventions". In Kerala, major nearshore lagoon and estuarine envircr.ments". Leaves mangrove occurrences are reported at Veli, Kollam, of many mangroves possess halophilic properties with Kumarakom, Kochi, Chetwai, Nadakavu, Edakkad, a thick cuticle and large mucilage cells. Buttress roots, Pappinisseri, Kannur and Chiteri (Fig. I). Present knee roots, stilt roots and vertical pneumatophores study has been undertaken to examine the heavy metal 211Corresponding author , l'rcscut address: Ikpartment of Mining and Geology, Kozhikode-673 020, Kerala. India 10281022 INDIAN J MAR SCI VOL. 43 (6), JUNE 2014 ecosystems of the state, viz., Veli, Kochi and Kannur mangroves. Materials and Methods Three mangrove fields located at Veli, Kochi and Kannur of Kerala state are chosen for the present investigation (Fig.1). Mangroves of Veli spread near the mouth of Veli lake. In the Kochi and Kannur mangroves spread is noticed in landward margins and islands of the coastal logoons. All the these three mangrove fields host distinct suites of mangrove vegetation. Most dominant mangrove/mangrove associated plants covering more than 70% of the mangrove vegetation are Acrostichum aureum, Barringtonia racemosa, Acanthus ilicifolius and Avicennia officinalis in the Veli mangroves; Avicennia officinalis, Rhizophora mucronata, Excoecaria agallocha and Acanthus ilicifolius in Kochi mangroves and Avicennia marina, Excoecaria agallocha, Derris trifoliata and Acanthus ilicifolius in Kannur mangroves16,17. Table 1 shows the various Fig. 1–Major mangrove occurrences in Kerala (after mangroves and mangrove associated plants whose Ramachandran and Mohanan 1991). vegetal parts have been selected for heavy metal analysis. accumulations in the vegetal parts (leaves and stems) of mangroves and mangrove associated plants in Field work was carried out in the Veli, Kochi and comparison to sediments in three important mangrove Kannur mangroves for the collection of surface Table 1–The mangroves and mangrove associated plants of Veli, Kochi and Kannur areas sampled for the present study. Sl. No. Veli mangroves Kochi mangroves Kannur mangroves (8º30’- 8º31’30’’N ; ( 9º59’- 10º11’30’’N ; (12º3’30’’- 12º5’30’’N ; 76º52’30’’- 76º54’E) 76º14’- 76º16’E) 75º13’- 75º14’30’’E) 1. * Acrostichum aureum *Avicennia officinalis * Avicennia marina 2. *Barringtonia racemosa *Rhizophora mucronata *Excoecaria agallocha 3. *Acanthus ilicifolius * Excoecaria agallocha * Derris trifoliata 4. *Avicennia officinalis *Acanthus ilicifolius * Acanthus ilicifolius 5. Vitis vitigenia Bruguiera gymnorrhiza Rhizophora mucronata 6. Sonneratia caseolaris Kandelia candel 7. Derris trifoliata Avicennia officinalis 8. Cerbera odollam Acrostichum aureum 9. Premna serratifolia Rhizophora apiculata *Most common species covering >70% of total population in the area BADARUDEEN et al: ENVIRONMENTAL SIGNIFICANCE OF HEAVY METALS 10291023 sediment samples, vegetal parts (leaves and stems) and other relevant field data for the study. Sand, silt and clay contents of the sediments were estimated following the method of Lewis18. The wet oxidation method of El Wakeel and Riley19 was applied for sediment organic carbon estimation. Representative, matured leaves as well as stem of the mangroves and mangrove associated plants were chosen for heavy Fig. 2–Ternary diagram showing sediment types of Veli, metal analysis. Ashed (at 500ºC) vegetal parts (i.e. Kochi and Kannur mangroves. S Sand, C Clay, M Mud, Z Silt, leaves and stems) and dried, powdered sediment cS Clayey sand, mS Muddy sand, zS Silty sand, sC Sandy clay, sM Sandy mud and sZ Sandy silt. samples were decomposed using HF-HClO4-HNO3 acid mixture and analysed for heavy metal composition and organic carbon loading. The content concentrations using Atomic Absorption of sand is almost similar in Veli (av. 66%) and Kochi Spectrophotometer following Rantala and Loring20. (av. 66.5%) mangroves; whereas the sand content is Metal data were checked against the international slightly lower (av. 53%) in Kannur mangroves; standards G2 and W1 and, it was found that the (Table 2). Figure 2 shows the ternary diagram showing accuracy of the analysis was ± 5% for Pb and Cu, ± the sediment types of Veli, Kochi and Kannur 10% for Zn and Mn and ± 20% of Co and Cd with mangroves. In general, muddy sand, silty sand and respect to certified values. sandy mud are the dominant sediment types of these Results and Discussions mangrove environments. Average organic carbon content in Veli, Kochi and Kannur mangroves are Sediment characteristics 3.71%, 2.62%, 4.01%, respectively. Strong positive The sediments in the Veli, Kochi and Kannur correlation of organic carbon with mud contents mangroves vary considerably in their granulometric existing in the sediments of Veli, Kochi and Kannur Table 2–Ranges and averages of sand, silt and clay contents in the surface sediments of Veli, Kochi and Kannur mangroves along with concentration of organic carbon and heavy metals. Sample location Sand Silt Clay C-org Fe Mn Co Pb Cd Cu Zn (%) (ppm) Veli mangroves Maximum 96.94 71.79 35.10 7.29 1.95 388 55 103 2 81 86 Minimum 8.74 5.32 3.87 0.32 0.56 27 11 16 1 20 22 Average 66.00 20.00 14.00 3.71 1.01 162 30 48 1 40 62 Kochi mangroves Maximum 93.33 50.83 27.69 4.89 7.00 171 141 56 3 71 91 Minimum 27.10 5.86 0.80 0.52 1.56 40 12 11 <1 12 15 Average 66.50 23.50 11.00 2.62 4.50 98 93 31 2 41 39 Kannur mangroves Maximum 79.97 50.11 32.33 6.03 5.49 334 70 39 6 77 87 Minimum 23.86 12.37 5.35 1.99 2.30 262 20 17 1 19 48 Average 53.00 29.00 18.00 4.01 3.71 295 52 28 2 47 66 10241030 INDIAN J MAR SCI VOL. 43 (6), JUNE 2014 mangroves (Fig.3) reveals the ability of finer detritus in the mangrove environments to trap organic matter reaching the area from autochthonous (mainly from litter fall of mangrove and mangrove associated plants) and allochthonous (brought from distant places through channel networks) sources. The increased fertility of the sediments by the way of organic matter accumulation could promote fast spreading of mangrove vegetation on one side and the stabilization of lands on the other21. Heavy metals in mangrove leaves and stems Table 3 shows the results of the heavy metal analysis of mangroves and mangrove associates of the Veli along with that of the Kochi and Kannur mangroves. Out of the 9 species subjected heavy metal analysis, four species viz; as Acrostichum aureum, Barringtonia racemosa, Acanthus ilicifolius and Avicennia officinalis, cover more than 75% of the Veli mangroves. Therefore, these plants have a significant bearing on the biogeochemical cycling of heavy metals in the Veli mangroves. Concentration of Fe in the leaf of the mangroves and mangrove associated plants of Veli region varies considerably between 0.41% (Acanthus ilicifolius) and 1.65% (Sonneratia caseolaris). The content of Fe in the stem varies between 0.81%, (Avicennia officinalis) and 1.28% (Derris trifoliata). Manganese exhibits wide variation both in leaves and, in stems of the Veli mangroves. Cerbera odollam shows the highest Mn content (5413 ppm) in its leaves compared to the other species (Table 3). The lowest concentration of Mn (495 ppm) is recorded for the species Avicennia officinalis. Like leaves, the stem of Cerbera odollam also accounts for higher Mn contents (6073 ppm). Lowest value (258 ppm) is recorded in Acrostichum aureum.