diff --git a/NAMESPACE b/NAMESPACE
index 7ceaf9c..8fc7e8f 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -20,6 +20,9 @@ export(abs_to_rel)
 export(albarede_juteau_1984)
 export(as_ASTR)
 export(at_to_wt)
+export(bdl_strategy_default)
+export(bdl_strategy_negative)
+export(bdl_strategy_none)
 export(copper_alloy_bb)
 export(copper_alloy_pollard)
 export(copper_group_bray)
diff --git a/R/ASTR_basic.R b/R/ASTR_basic.R
index b894e40..9aad994 100644
--- a/R/ASTR_basic.R
+++ b/R/ASTR_basic.R
@@ -12,8 +12,8 @@
 #' \itemize{
 #'   \item **as_ASTR**: Transforms an R `data.frame` to an object of class
 #'   `ASTR`.
-#'   \item **read_ASTR**: Reads data from a file (.csv, .xls, .xlsx) into
-#'   an object of class `ASTR`.
+#'   \item **read_ASTR**: Reads data from a file (.csv, .xls, .xlsx) and
+#'   converts it into an object of class `ASTR`.
 #'   \item **validate**: Performs additional validation on `ASTR` and returns
 #'   a `data.frame` as a workable list of potential issues.
 #'   \item **get_..._columns**: Subsets `ASTR` tables to columns of a certain
@@ -33,10 +33,10 @@
 #' @param id_column name of the ID column. Defaults to "ID"
 #' @param context columns that provide contextual (non-measurement) information;
 #'   may be column names, integer positions, or a logical inclusion vector
-#' @param bdl strings representing “below detection limit” values. By default,
-#'   the following are recognized: "b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"
-#' @param bdl_strategy function used to replace BDL strings. Defaults to a
-#'   static function returning `NA`
+#' @param bdl_strategy function used to replace "below detection limit" strings.
+#'   See [bdl_strategies] for the different available strategies and on how to
+#'   implement a custom one. Use [purrr::compose()] to combine different
+#'   [bdl_strategies] (see examples).
 #' @param guess_context_type should appropriate data types for contextual
 #'   columns be guessed automatically? Defaults to `TRUE`
 #' @param na character vector of strings to be interpret as missing values. By
@@ -66,18 +66,10 @@
 #'   unless `drop_columns = TRUE` (then it will result in warnings for the
 #'   respective columns).
 #'
-#'   Below detection limit notation (i.e. ‘b.d.’, ‘bd’, ‘b.d.l.’, ‘bdl’, ‘<LOD’,
-#'   or ‘<..’) for element and oxide concentrations is specified using the `bdl`
-#'   argument. One or more notations can be used as is appropriate for the
-#'   dataset, and can be notations not included in the list above. The argument
-#'   `bdl_strategy` is used to specify the value for handling detection limits.
-#'   This is to facilitate the different handling needs of the detection limit
-#'   for future statistical applications, as opposed to automatically assigning
-#'   such values as ‘NA’.
-#'
 #'   Missing values are allowed anywhere in the data file body, and will be
 #'   replaced by `NA` automatically.
 #'
+#'
 #' @examples
 #' library(magrittr)
 #'
@@ -92,6 +84,11 @@
 #' # validating an ASTR table
 #' validate(arch)
 #'
+#' # combining bdl strategies
+#' arch2 <- as_ASTR(test_df, id_column = "Sample", context = 1:7,
+#'   bdl_strategy = purrr::compose(bdl_strategy_default, bdl_strategy_negative)
+#' )
+#'
 #' # extracting subsets of columns
 #' conc <- get_concentration_columns(arch) # see also other get_..._columns functions
 #'
@@ -120,12 +117,7 @@
 #' @export
 as_ASTR <- function(
   df, id_column = "ID", context = c(),
-  bdl = c("b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"),
-  bdl_strategy = function() NA_character_,
-  # this only allows static functions, essentially: bdl_replace = "NA"
-  # in case more sophisticated handling is desired:
-  # bdl_strategy = function(x, colname) { bdl_lookup_table[colname] / sqrt(2) }
-  # bdl_lookup_table = c("Fe_%" = 3)
+  bdl_strategy = bdl_strategy_default,
   guess_context_type = TRUE,
   na = c(
     "", "n/a", "NA", "N.A.", "N/A", "na", "-", "n.d.", "n.a.",
@@ -166,7 +158,7 @@ as_ASTR <- function(
     dplyr::ungroup()
   # determine and apply column types
   column_table <- parse_colnames(df2, context, drop_columns)
-  constructors <- build_constructors(column_table, bdl, bdl_strategy, guess_context_type, na)
+  constructors <- build_constructors(column_table, bdl_strategy, guess_context_type, na)
   col_list <- purrr::map2(df2, constructors, function(col, f) f(col)) %>%
     purrr::discard(is.null)
   df3 <- as.data.frame(col_list, check.names = FALSE)
@@ -222,8 +214,7 @@ read_ASTR <- function(
     "", "n/a", "NA", "N.A.", "N/A", "na", "-", "n.d.", "n.a.",
     "#DIV/0!", "#VALUE!", "#REF!", "#NAME?", "#NUM!", "#N/A", "#NULL!"
   ),
-  bdl = c("b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"),
-  bdl_strategy = function() NA_character_,
+  bdl_strategy = bdl_strategy_default,
   drop_columns = FALSE,
   validate = TRUE,
   ...
@@ -284,7 +275,7 @@ read_ASTR <- function(
   as_ASTR(
     input_file,
     id_column = id_column, context = context,
-    bdl = bdl, bdl_strategy = bdl_strategy,
+    bdl_strategy = bdl_strategy,
     guess_context_type = guess_context_type, na = na,
     drop_columns = drop_columns,
     validate = validate
diff --git a/R/ASTR_bdl_strategies.R b/R/ASTR_bdl_strategies.R
new file mode 100644
index 0000000..3173c40
--- /dev/null
+++ b/R/ASTR_bdl_strategies.R
@@ -0,0 +1,40 @@
+#' @name bdl_strategies
+#'
+#' @title Strategies to replace "below detection limit" values
+#'
+#' @description ...
+#'
+#' @param x a vector, derived from a data.frame column
+#' @param colname name of the respective data.frame column
+#' @param marker values indicating "below detection limit"
+#' @param value value to replace values identified as "below detection limit"
+#' @param ... further arguments passed to or from other methods
+#'
+#' @rdname bdl_strategies
+#'
+#' @examples
+#' plot(1,1)
+#'
+NULL
+
+#' @rdname bdl_strategies
+#' @export
+bdl_strategy_default <- function(x, colname, marker = c("b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"), ...) {
+  bdl_indices <- which(grepl(paste(marker, collapse = "|"), x, perl = FALSE))
+  x[bdl_indices] <- NA_character_
+  return(x)
+}
+
+#' @rdname bdl_strategies
+#' @export
+bdl_strategy_none <- function(x, colname, ...) {
+  return(x)
+}
+
+#' @rdname bdl_strategies
+#' @export
+bdl_strategy_negative <- function(x, colname, value = NA_character_, ...) {
+  bdl_indices <- which(grepl("^-\\d*\\.?\\d*\\*?\\d*\\^?\\-?\\d*$", x))
+  x[bdl_indices] <- value
+  return(x)
+}
diff --git a/R/ASTR_colname_parser.R b/R/ASTR_colname_parser.R
index 506839a..d8afe96 100644
--- a/R/ASTR_colname_parser.R
+++ b/R/ASTR_colname_parser.R
@@ -206,7 +206,7 @@ parse_colnames <- function(x, context, drop_columns) {
 # 2. build constructor functions
 build_constructors <- function(
   column_table,
-  bdl, bdl_strategy,
+  bdl_strategy,
   guess_context_type, na
 ) {
   purrr::pmap(
@@ -224,7 +224,7 @@ build_constructors <- function(
         function(x) {
           # bdl
           if (consider_bdl) {
-            x <- apply_bdl_strategy(x, colname, bdl, bdl_strategy)
+            x <- bdl_strategy(x = x, colname = colname)
           }
           # type
           if (type == "numeric") {
@@ -268,14 +268,6 @@ as_numeric_info <- function(x, colname) {
   return(y)
 }
 
-# colname only an argument in case we want to implement more specific handling
-# eventually
-apply_bdl_strategy <- function(x, colname, bdl, bdl_strategy) {
-  bdl_values <- which(grepl(paste(bdl, collapse = "|"), x, perl = FALSE))
-  x[bdl_values] <- bdl_strategy()
-  return(x)
-}
-
 #### regex validators ####
 
 is_err_percent <- function(colname) {
diff --git a/man/ASTR.Rd b/man/ASTR.Rd
index 91da787..53245ed 100644
--- a/man/ASTR.Rd
+++ b/man/ASTR.Rd
@@ -24,8 +24,7 @@ as_ASTR(
   df,
   id_column = "ID",
   context = c(),
-  bdl = c("b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"),
-  bdl_strategy = function() NA_character_,
+  bdl_strategy = bdl_strategy_default,
   guess_context_type = TRUE,
   na = c("", "n/a", "NA", "N.A.", "N/A", "na", "-", "n.d.", "n.a.", "#DIV/0!", "#VALUE!",
     "#REF!", "#NAME?", "#NUM!", "#N/A", "#NULL!"),
@@ -42,8 +41,7 @@ read_ASTR(
   guess_context_type = TRUE,
   na = c("", "n/a", "NA", "N.A.", "N/A", "na", "-", "n.d.", "n.a.", "#DIV/0!", "#VALUE!",
     "#REF!", "#NAME?", "#NUM!", "#N/A", "#NULL!"),
-  bdl = c("b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"),
-  bdl_strategy = function() NA_character_,
+  bdl_strategy = bdl_strategy_default,
   drop_columns = FALSE,
   validate = TRUE,
   ...
@@ -83,11 +81,10 @@ unify_concentration_unit(x, unit, ...)
 \item{context}{columns that provide contextual (non-measurement) information;
 may be column names, integer positions, or a logical inclusion vector}
 
-\item{bdl}{strings representing “below detection limit” values. By default,
-the following are recognized: "b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"}
-
-\item{bdl_strategy}{function used to replace BDL strings. Defaults to a
-static function returning \code{NA}}
+\item{bdl_strategy}{function used to replace "below detection limit" strings.
+See \link{bdl_strategies} for the different available strategies and on how to
+implement a custom one. Use \code{\link[purrr:compose]{purrr::compose()}} to combine different
+\link{bdl_strategies} (see examples).}
 
 \item{guess_context_type}{should appropriate data types for contextual
 columns be guessed automatically? Defaults to \code{TRUE}}
@@ -139,8 +136,8 @@ interact with them.
 \itemize{
 \item \strong{as_ASTR}: Transforms an R \code{data.frame} to an object of class
 \code{ASTR}.
-\item \strong{read_ASTR}: Reads data from a file (.csv, .xls, .xlsx) into
-an object of class \code{ASTR}.
+\item \strong{read_ASTR}: Reads data from a file (.csv, .xls, .xlsx) and
+converts it into an object of class \code{ASTR}.
 \item \strong{validate}: Performs additional validation on \code{ASTR} and returns
 a \code{data.frame} as a workable list of potential issues.
 \item \strong{get_..._columns}: Subsets \code{ASTR} tables to columns of a certain
@@ -170,15 +167,6 @@ not recognised as an analytical column, this will result in an error,
 unless \code{drop_columns = TRUE} (then it will result in warnings for the
 respective columns).
 
-Below detection limit notation (i.e. ‘b.d.’, ‘bd’, ‘b.d.l.’, ‘bdl’, ‘<LOD’,
-or ‘<..’) for element and oxide concentrations is specified using the \code{bdl}
-argument. One or more notations can be used as is appropriate for the
-dataset, and can be notations not included in the list above. The argument
-\code{bdl_strategy} is used to specify the value for handling detection limits.
-This is to facilitate the different handling needs of the detection limit
-for future statistical applications, as opposed to automatically assigning
-such values as ‘NA’.
-
 Missing values are allowed anywhere in the data file body, and will be
 replaced by \code{NA} automatically.
 }
@@ -196,6 +184,11 @@ arch <- as_ASTR(test_df, id_column = "Sample", context = 1:7)
 # validating an ASTR table
 validate(arch)
 
+# combining bdl strategies
+arch2 <- as_ASTR(test_df, id_column = "Sample", context = 1:7,
+  bdl_strategy = purrr::compose(bdl_strategy_default, bdl_strategy_negative)
+)
+
 # extracting subsets of columns
 conc <- get_concentration_columns(arch) # see also other get_..._columns functions
 
diff --git a/man/bdl_strategies.Rd b/man/bdl_strategies.Rd
new file mode 100644
index 0000000..52a2b89
--- /dev/null
+++ b/man/bdl_strategies.Rd
@@ -0,0 +1,38 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/ASTR_bdl_strategies.R
+\name{bdl_strategies}
+\alias{bdl_strategies}
+\alias{bdl_strategy_default}
+\alias{bdl_strategy_none}
+\alias{bdl_strategy_negative}
+\title{Strategies to replace "below detection limit" values}
+\usage{
+bdl_strategy_default(
+  x,
+  colname,
+  marker = c("b.d.", "bd", "b.d.l.", "bdl", "<LOD", "<"),
+  ...
+)
+
+bdl_strategy_none(x, colname, ...)
+
+bdl_strategy_negative(x, colname, value = "99999", ...)
+}
+\arguments{
+\item{x}{a vector, derived from a data.frame column}
+
+\item{colname}{name of the respective data.frame column}
+
+\item{marker}{values indicating "below detection limit"}
+
+\item{...}{further arguments passed to or from other methods}
+
+\item{value}{value to replace values identified as "below detection limit"}
+}
+\description{
+...
+}
+\examples{
+plot(1,1)
+
+}
diff --git a/vignettes/ASTR.showcase.Rmd b/vignettes/ASTR.showcase.Rmd
index c0429f9..9b6deb9 100644
--- a/vignettes/ASTR.showcase.Rmd
+++ b/vignettes/ASTR.showcase.Rmd
@@ -57,7 +57,7 @@ data
 
 Note how the column headers are organised according to the ASTR conventions. This allows the package to _understand_ some of the semantics of the dataset in the `read_ASTR()` process, and correctly represent them in the resulting `ASTR` object. A closer look at the mock-up data also reveals (common) problems with the copper isotope data: it seems that some Excel formulas did not work as intended and left `#REF!` entries. `read_ASTR()` will read these as `NA` values. Finally, every `ASTR` object requires one column that acts as a unique row identifier. In this dataset there is no such column, though, only a `Group` identifier. `read_ASTR()` can automatically turn such a column to a unique identifier.
 
-We can now perform the reading process. As we are working with mock-up data in an R vignette, we do not read from the file system. We only need to call an essential internal function of `read_ASTR()`: `as_ASTR()`. It turns R data.frames to `ASTR` objects. If we would start from an Excel file we would call `read_ASTR()` instead.
+We can now perform the reading process. As we are working with mock-up data in an R vignette, we do not read from the file system. We only need to call an essential internal function of `read_ASTR()`: `as_ASTR()`. It turns R data.frames to `ASTR` objects. If we would start from an Excel file we would call `read_ASTR()` instead, which internally calls `as_ASTR()` to convert the data into an ASTR object after reading the file.
 
 To do this in practice, we not only have to submit our `data` to `as_ASTR()`, but also set two other arguments: 1. We have to define one of the columns as the ID column with `id_column`, and 2. we explicitly have to mark any column providing contextual information with `context` (i.e. no analytical values, cf. [ASTR schema: Implementation](VG.ASTR.Schema.Implementation.html)).