Tissue Contaminants

Benthos sample collection for contaminants analysis

The Van Veen grab was attached to the vessel’s cable and winch system and lowered to 2-3 meter above the sediment surface. The vessel was then manoeuvred into position above the target location. Once in position, the grab was lowered to the bottom where it triggered and closed upon contact with the sediment surface. The full grab was raised back up slowly to the vessel and landed on a stainless steel elevated chute for emptying into the sample container. 

Once a sample is deemed acceptable, a picture of the sample (in the grab with the flaps lifted) is taken, and then the sample placed in a tote for screening. It is important that the sample be rinsed out in its entirety into the tote. This sample must be labelled, at minimum, with a label inside in the sample tote, in the sample itself. It is also useful to label the outside of the tote.

The sample totes are rinsed with seawater, then a mild hydrochloric acid (5%) solution before each sample was taken.   The screens (see below) and picking tools were also rinsed with HCL and acetone to remove any remaining organic material after each grab. Used acetone was collected in the field and disposed of in an appropriate way back on land. 

Extreme care must be taken during washing of samples to avoid breakage of specimens. 

Screening using seawater is done immediately after collection, as specimens can start to die and decompose within ~6 hours after collection, depending on the air temperature.  All samples were screened and processed on board before the end of the work day.  

Biologica’s screening system consists of an aluminum stand with stacked trays and a seawater pump (battery operated when used on board a ship) with an intake and outflow hose (Fig. 1). The washing stand includes a chute for directing the wash-water screened mud/silt off the deck of the boat (or side of the dock). This stand should be secured to the side of the boat or the edge of the dock during screening, with the chute directed overboard/over the edge of the dock. Generally one 1.0mm screen is placed on the top of the screen and is the only screen used. If additional fractions are being collected, is it is important to place the plastic flaps on the screen to direct the sample into the tray underneath. 

The battery-operated seawater pumps require the use of a 12V battery. Seawater pumps have water flow from 1.5-2 gallons per minute (gpm) (old pumps) or 3-4 gph (new pumps). Flow on the pumps was adjusted with the ball valve to ~2 gallons per minute so it is a gentle flow and does not cause damage to the organisms. Spray nozzles should not be used for this reason. 

The intake hose has an attachment on the end with a 250 mm screen that prevents planktonic organisms or other debris from entering the sample.  This “hose-end” also has a check valve that prevents backflow of water.

Samples are washed in portions to minimize the opportunity for animals to become fragmented on the screen.  The washer holds the tote containing the sample on the edge of the washing stand, and puts the hose into the sample itself, breaking up the sample inside the tote. Thus most of the washing takes place in the tote itself, with the overflow containing debris that is retained on the screen. The unwashed sample should NOT be placed directly on the screen. If a large volume of unscreened debris on the screen requires washing, this not only creates damage to organisms, but also is often much slower, and results in samples that are not as well-screened.  Once the portion on the screen has been washed thoroughly the sediment was washed off the screen and a new portion placed for picking.

Large, heavy debris such as rocks are removed immediately to prevent damage to organisms.  Any attached organisms are picked off and placed on an acetone washed film of aluminum foil.  Further large, visible fragile organisms in the sediment (e.g., brittle stars, nemertean worms, some tubeworms, scaleworms) were removed next and placed on the aluminum foil.  After these steps, all visible organisms are removed using forceps and placed on the foil. This process takes up to 3 hours for each location (2-3 grabs composited).  When complete, the organisms picked out of the grab are placed in acetone rinsed glass jars with teflon-coated lids, labelled appropriately inside and out of the jar and packed on ice.  Any large samples of shelled organisms  should be wrapped in foil (for organic contaminants analysis) then placed in ziploc bags.  Samples for metals analyses are simply placed in ziploc bags without foil.  Samples are placed in a deep-freeze (-4oC) after each field day.  A minimum of 20 g wet weight for one jar, plus an additional 10 g for a second jar should ideally be collected.