Introduction high yield with low heavy metal accumulation.

Introduction

Pakistan
once a water surplus country, is now in the list of water deficit countries. Water
availability is decreasing drastically from 1299m3 in 1996-1997 to
11,00m3 in 2006 and it will be decreased to about 700m3
in the near 2025. Therefore, most of the people rely on the non-conventional
water resources i.e.  Industrial waste water,
for irrigation practices (Ghulam Murtaza and Munir H. Zia). Irrigation with
waste water may result in a number of benefits and can change the soil
chemistry as well. Potential beneficial changes may be, increase in available
phosphorus, potassium, nitrogen and organic carbon when compared with soil treated
with clean irrigation water (36 in Agarwal). In many cases irrigation with
waste water resulted in increased growth, yield and plant constituents as well
(2 in agarwal).

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Due
to uninterruptedly increasing population, very large amount of waste water is
produced on daily basis from houses, markets and as well as from industries (4
in 30-36). By reusing this huge amount of water for agricultural irrigation
purpose will result in less dependence on freshwater resources. (2 in 30-36).
Waste water pollution is now a major problem which should be handled at our
first priority to stop the depleting freshwater resources (3 in 30-36).

Lactuca sativa
L. belongs to largest family of an angiosperms, Asteraceae. It is most
important leafy vegetable which is exclusively used as a salad but some varieties
are also cooked. (Zahr). Lettuce is a cool season crop and grows best in
temperature range of 73oF at day time and 45oF at night.
Silt loams and sandy soils are the best soil for growing lettuce.

One
major threat associated with the use of waste water is the accumulation of
heavy metals by plants (44 in agarwal). Therefore this study was carried out to
evaluate the effect of waste water on morphological and physiological
characters of lettuce (Lactuca sativa L.). It is hypothesized that proper ratio
of waste water and freshwater may result in vigorous growth and high yield with
low heavy metal accumulation. Moreover, by filtering the waste water with bio
filter may result in a waste water with low potential threat to heavy metal
accumulation as well.

 

Materials and Methods

Area of Study

This
experiment was carried out in PMAS Arid Agriculture University Rawalpindi
(33.6492° N, 73.0815° E) to access the impacts of industrial waste water (Lai
Stream, Rawalpindi) on morphological, biochemical and physiological properties
of two varieties of Lactuca sativa L.
namely L. sativa var. Iceberg and
Boston. This experiment was
conducted in pots with dimeter of 14″ length and 8″of width. F1 generation
plants of two lettuce varieties were provided by the National agriculture
research council Islamabad.  In each pot
four seedlings were transplanted and properly watered at transplantation time.
Experiment was conducted in totally randomized block design and all the
treatments were in three replicates. Watering was done thrice in a week. Plants
which were given well water were taken as control. Detail of the treatment is
given in the table.

Sampling of Wastewater

Wastewater
was collected from the I-9 industrial area of Islamabad. All the industrial and
domestic wastewater of I-8 and I-9 area is drained into this stream. A compost
sample was taken and brought into the experimental sight. Waste water was then
filtered with the help of biofilter for further treatments. Sampling was made
two times during the study, first at start of the experiment and secondly after
25 days of sowing. Collected wastewater was analyzed for its physico-chemical
properties in the lab.

Parameter

Value

ISI Standards

pH

8.02

5.5-9.0

Total solids (mg l-1)

6380

Total dissolved solids (mg l-1)

6180

2100

Total suspended solids (mg l-1)

200

100

Hardness (mg l-1)

1130

600

Chlorides (mg l-1)

1350

1000

Table 1. Some physio-chemical
properties of wastewater sample from Lai stream

S.no

Row

Treatments

1

To

100% irrigation water
(Control)

2

T1

75% IW+ 25% WW

3

T2

50%IW+ 50%ww

4

T3

25% IW + 75% WW

5

T4

100 % Wastewater

6

T5

75% IW + 25% FW

7

T6

50% IW + 50% FW

8

T7

25% IW+  75%FW

Table 2. Treatments of the
wastewater and filtered water

Parameters

Value

ISI standards

Copper

0.21

0.05-1.5

Chromium

2.03

0.05

Nickel

1.59

<0.01 Zinc 0.46 5.0 - 15.0 *ISI standards No. 2490 (1974) Table 3. Heavy metals concentration (mg l-1) in industrial wastewater samples Lai Stream Rawalpindi Soil Analysis Composite soil sample was collected after harvesting and stored in a plastic bottle for further analysis. The soil sample was analyzed for different physico chemical properties like pH, EC, total organic content etc. Texture Bulk density (g cc-1) pH Organic matter (%) CaCO3 (%) E.C. (dS m-1) Heavy metals (ppm) Loamy 1.40 7.20 0.53 0.60 1.60 Zn Cu Ni Cr 0.26 0.72 0.18 0.12 E.C. = Electrical conductance Table 4: Physico-chemical properties of alluvial soil before sowing   Results and Discussion Leaf Chlorophyll Content: With increase in wastewater concentration upto 50%, leaf chlorophyll contents increased and then decreased with further increase in wastewater concentration. Also Iceberg variety was more effected than Boston (Table 5). Naaz and S.N. Pandey (2009) and Jenkins et al. (1994) observed that plant irrigated by wastewater had darker green color than control and had lower chlorophyll contents when concentration was increased beyond 50%. When bio-filtered was applied, chlorophyll contents increased but similar pattern was observed. Table5. Chlorophyll Contents after treatment with wastewater   Leaf Area: By increasing wastewater to irrigational water ratio to 50%, leaf area was increased, but it then rapidly decreased when exposed to 75% and 100% wastewater (Table 6). When bio-filtered water was applied, it was observed that leaf area increased by 8% in Boston and 13% in Iceberg. Alizade et al. (2001) reported that wastewater increased leaf width in maize (Zea mays). Wastewater contains a great number of essential nutrients for increasing plant leaf area. Table 6. Leaf area after treatment with wastewater   Root Fresh weight: Root fresh weight increased with increase in wastewater concentration in both varieties upto 50% and then decreased upto 100% concentration. Wastewater contains essential nutrients increasing cell volume and turgor so leaf weight increases (Jalali et al., 2010). By exposing the plants to bio-filtered water, relative weight increased indicating the removal of some nutrients by bio-filter (Table 7). Table 7. Root fresh weight after exposure to wastewater   Shoot Fresh Weight: Increase in shoot fresh weight was observed when exposed upto 50% concentration in both varieties but it then decreased when exposed to higher concentration. Wastewater contains essential nutrients increasing cell volume and turgor so leaf weight increases (Jalali et al., 2010). By exposing the plants to bio-filtered water, relative weight increased indicating the removal of some nutrients by bio-filter (Table 8).   Table 8. Shoot fresh weight after wastewater treatment   Root Length: Plant irrigated with wastewater shown considerable root elongation upto 50% concentration and then it decreased upto 100% concentration in both varieties. When they were irrigated with bio-filtered water root length increased sufficiently then untreated wastewater (Table 9). Table 9. Effect of wastewater on Root length   Shoot Length: Plant irrigated with wastewater shown considerable shoot elongation upto 50% concentration and then it decreased upto 100% in both varieties. The retardation in growth and development of toxicity symptoms in plants could be attributed due to high uptake of heavy metals and their accumulation in plant parts (Pandey, 2006).When they were irrigated with bio-filtered water shoot length increased sufficiently then untreated wastewater (Table 10). Table 10. Effect of wastewater on Shoot length   Conclusion This study concluded that wastewater of Lai stream is not suitable for irrigational purposes without filtration as it contains high concentration of heavy metal, and it may enter human food chain, if plants are directly irrigated with this water. Lactuca sativa L. was found to be affected by the undiluted wastewater and produced visible symptoms of toxicity indicating its sensitive nature to pollution thus can be used in phytoremediation studies.

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