**3.3 Phytoremediation by submerged aquatic weeds**

Among the submerged aquatic weeds *Hydrilla verticillata*, *Ceratophyllum dermersum, Potamageton crispus, Valisnaria natans, Eleocharis acicularis* and *Elodea Canadensis* widely reported by many researchers to extract As from contaminated water. Studies conducted in laboratory and field conditions indicated that *Hydrilla verticillata*, and *Ceratophyllum demersum* can uptake higher proportion of As from contaminated water depending on exposure time and concentration of metalloid [22, 56, 57]. Unlike *Spirodela polyrhiza*, *Hydrilla verticillata* also uptake

#### **Figure 2.**

*Arsenic uptake comparison between various weed plants (Hydrilla, Ceratophyllum, Wolffia, Lemna and Eicchornia) grown in singly or in various combinations upon arsenic exposure for 30 days (adapted from Srivastava et al., 2014).*

#### *Phytoremediation of Arsenic Contaminated Water Using Aquatic, Semi-Aquatic and Submerged... DOI: http://dx.doi.org/10.5772/intechopen.98961*

more arsenite (As3+) form rather arsenate (As5+) form [50]. Under simulated field condition (aquatic pond) Hydrilla verticillata alone removed sum total 8546 μg (348 μg g−1) of As from contaminated water (As concentration 1500 μg L−1) which is 72% of the total arsenic supplied [56]. Ceratophyllum demersum reported to accumulate 76 μg g−1 in 4 days and and As accumulation further increased to 201 μg g−1 in 7 days when exposed to 50 μM As solutions [22]. Maximum As accumulation by Ceratophyllum was recorded 525 μg g−1 dw when subjected to with 250 μM As5+ solution for 7 days [22]. Uptake of As by *Ceratophyllum demersum* depends on species of As present (As3<sup>+</sup> vs. As5+) and pH of the medium. Maximum uptake of As3+ by Ceratophyllum was reported at pH 6.5 [58]. This variation in selective uptake of As species largely depends on uptake pathways and plant metabolism.

In natural conditions, submerged weeds grow in water bodies in association with floating macrophytes. Use of Combinations of submerged and floating weeds found more effective for phytoremediation purpose than submerged and floating weeds alone. Research work carried out using Hydrilla, Certophyllum, lemna and Wolfia at various combinations showed that Ceratophyllum + lemna combination (3326 μg) combination removed maximum total As followed by *Hydrilla + Wolfia* (1896 μg) (**Figure 2**). When the contribution of single plant considered, contribution of Hydrilla is more than 50% [56]. Arsenic phytoextraction potential of five different submerged weeds namely *Ceratophyllum dermersum*, *Potamageton crispus, Myriophyllum spicatum, Hydrilla verticillata* and *Vallisneria natans* were compared


#### **Table 1.**

*Phytoremediation ability of various aquatic and semi aquatic weeds.*

under natural As contaminated environement [59]. Results showed that all plants accumulated more 1000 mg kg−1 dw As; highest and lowest As accumulation and BCF were associated with *Vallisneria natans* (BCF- 361) and *Ceratophyllum dermersum* (BCF- 221) [59]. Similarly ability of potamogeton spp., Myriophyllum spp. and Valisnaria app to uptake As from contaminated water were also been reported by many authors [60–62]. Arsenic uptake by various types of aquatic, semi-aquatic and submerged weeds has been outlined in **Table 1**.
