MEVE 018: Unit 01 - Sampling and Preservation

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UNIT 1: SAMPLING AND PRESERVATION

1.0 Introduction

Environmental analysis begins with the critical step of sampling, which determines the quality and reliability of subsequent data and interpretations. Whether it is air, water, or soil, improper sampling can result in misleading outcomes. After collection, preservation, storage, and handling ensure the samples retain their integrity before analysis. This unit introduces the principles and protocols for effective sampling and preservation, crucial for environmental monitoring, pollution studies, and regulatory compliance.

1.1 Objectives

After completing this unit, learners will be able to:

  • Understand various sampling methods used in environmental monitoring.
  • Describe protocols for air, water, and soil sampling.
  • Identify proper sites, times, and frequencies for sampling.
  • Learn techniques for preserving environmental samples.
  • Comprehend best practices in storage and transportation of samples.
  • Apply Good Laboratory Practices (GLP) in environmental testing.

1.2 Types of Sampling and Their Methods

Sampling is the process of selecting a representative portion of the environment to analyze for specific parameters. Sampling can be broadly categorized into:

1.2.1 Grab Sampling

  • Instantaneous samples collected at a specific location and time.
  • Simple, cost-effective, and ideal for determining current conditions.

1.2.2 Composite Sampling

  • Combines several individual samples collected over time or space.
  • Useful for averaging pollutant concentrations over an area or period.

1.2.3 Systematic Sampling

  • Samples taken at regular intervals (time or space).
  • Minimizes sampling bias.

1.2.4 Stratified Sampling

  • The area is divided into different strata based on characteristics (e.g., land use), and samples are taken from each.
  • Improves representativeness.

1.2.5 Random Sampling

  • Each sampling location has an equal probability of being selected.
  • Eliminates selection bias.

1.3 Methods of Air, Water, Soil Sampling

1.3.1 Air Sampling

  • Passive Sampling: Relies on natural diffusion of pollutants (e.g., badge samplers).
  • Active Sampling: Uses pumps to pull air through filters or absorbing media.
  • Instruments: High Volume Samplers, Gas Monitors, PM Samplers.

1.3.2 Water Sampling

  • Manual Sampling: Bottles or samplers lowered into water bodies.
  • Automatic Samplers: Pre-programmed devices to collect at intervals.
  • Parameters include pH, DO, BOD, heavy metals, pesticides, etc.

1.3.3 Soil Sampling

  • Auger or Core Sampling: Extracts soil profiles for chemical analysis.
  • Grab Samples: Collected from surface layers.
  • Care taken to avoid contamination and ensure depth consistency.

1.4 Sampling Protocols – Selection of Sites

Proper site selection ensures that collected data reflects true environmental conditions. Factors to consider:

  • Purpose of study: Baseline data, pollution detection, trend monitoring.
  • Accessibility: Sites should be safe and reachable regularly.
  • Proximity to pollution sources: E.g., industrial plants, sewage outlets.
  • Hydrology and topography: Affects pollutant transport and distribution.
  • Replicates: Multiple sites reduce spatial variability errors.

1.5 Time and Frequency for Sampling

Sampling schedules should capture temporal variations due to weather, human activity, or seasonal changes.

  • Time of Day: Morning vs. afternoon values (e.g., air quality).
  • Frequency:
    • Routine Monitoring: Weekly, monthly, or seasonal sampling.
    • Event-Based: After rainfall, spills, or industrial discharges.
    • Continuous Monitoring: Automated stations for critical areas.

1.6 Preservation

Preservation involves stabilizing a sample's physical and chemical properties between collection and analysis. Techniques vary based on the type of sample and parameters measured.

Common Preservation Methods:

  • Cooling (4°C): Most biological and chemical samples.
  • Chemical Additives:
    • Nitric Acid (HNO₃): For heavy metals.
    • Sulfuric Acid (H₂SO₄): For nutrients or BOD.
    • Sodium Thiosulfate: For neutralizing chlorine in water.
  • pH Adjustment: Prevents microbial activity or chemical transformation.

Timely preservation reduces degradation and microbial action, ensuring accurate results.

1.7 Storage and Handling of Samples

Once preserved, samples must be handled carefully to avoid contamination or alteration.

Guidelines:

  • Use clean, sterilized, non-reactive containers (e.g., borosilicate glass, HDPE).
  • Label containers with sample ID, date, time, site, and preservation method.
  • Store samples in coolers or refrigerators if necessary.
  • Avoid exposure to light for light-sensitive compounds.
  • Maintain chain-of-custody records for legal and regulatory needs.
  • Analyze within holding time limits (e.g., 24 hours for BOD, 6 months for metals).

1.8 Good Laboratory Practices (GLP)

GLP refers to a quality system for ensuring reliability and reproducibility in laboratories.

Key Principles:

  • Documentation: Accurate record-keeping of procedures, observations, and results.
  • Calibration: Regular testing of instruments and tools.
  • Standard Operating Procedures (SOPs): Defined protocols for all procedures.
  • Training: Staff must be trained in safety, sampling, and analysis techniques.
  • Sample Management: Unique IDs, logs, and traceability of samples.
  • Quality Control (QC) and Quality Assurance (QA): Internal and external validation of methods and data.

GLP ensures data integrity and is critical for compliance with environmental regulations (e.g., EPA, CPCB).

1.9 Let Us Sum Up

  • Environmental sampling is fundamental for assessing and monitoring pollution.
  • Different sampling methods exist for air, water, and soil based on objectives.
  • Site selection, timing, and frequency must be carefully planned to reflect environmental variability.
  • Preservation techniques like cooling and chemical additives prevent sample degradation.
  • Proper storage and adherence to GLP maintain data accuracy and reliability.

1.10 Keywords

  • Sampling-The process of collecting a representative portion of an environmental medium.
  • Grab Sample-A single sample collected at a specific moment in time.
  • Composite Sample-A combination of samples taken over time or space to represent an average.
  • Passive Air Sampling-Air sampling without mechanical assistance; relies on diffusion.
  • Preservation-Methods used to stabilize sample characteristics before analysis.
  • Auger Sampler-A tool for collecting subsurface soil samples.
  • Holding Time-Maximum period between sample collection and analysis.
  • Chain-of-Custody-Documentation trail that tracks sample handling for legal/QA purposes.
  • Good Laboratory Practices (GLP)-Set of standards to ensure quality, reliability, and integrity in lab work.
  • Calibration-Adjustment of instruments to ensure accurate readings.

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