MATERIALS AND METHODS
Water and plant sampling in Tha Chin River
The study area was located in Samut
Sakhon, Nakhon Pathom, Suphan Buri and Chai
Nat provinces, in central Thailand, which has a
tropical monsoonal climate with an annual average
rainfall of 1,075 mm.yr-1 ([Available from: http://
www.dnp.go.th/Research/watershade/centre.
html]. [Sourced: 29/10/12]). Thirty-eight sampling
sites were selected along the Tha Chin River,
including sites in the estuary and sites in upstream
areas (Figure1). The sampling was carried out
during both the dry (March 2006) and high-loading
(November 2006) seasons. Water samples were
collected in each season from all sampling sites.
Samples of the plant I. aquatica were collected
at station 29 in October 2005 and were examined
to determine the heavy metal content in separate
parts namely, the leaf, stem and root. Although
I. aquatica and N. oleracea could not be found
at some study sites, additional I. aquatica and
N. oleracea samples were collected at 33 and 15
sampling sites in March 2006 (dry season) and
November 2006 (wet season), respectively. Only
edible parts of these plants (leaf and stem) were
analyzed for heavy metal contents.